This is a very annoying crash that has led to much frustration. It can't be reproduced with 100% reliability for all songs, but it can be, however, reproduced for the same song multiple times.

To reproduce:
1. Open banshee
2. Search for a particular track that you want to edit (in my case "Mastadon")
3. Go into the "Edit Track Information" dialog
4. Change some text (in my case, trying to change "Mastadon" to "Mastodon"... the crash happens as soon as I type the "o").

Here's the output, followed by the debug output:

guv@colada:~$ banshee-1
[Info  02:22:14.867] Running Banshee 1.4.1
[Warn  02:22:22.482] Cannot connect to NetworkManager - An available, working network connection will be assumed
[Info  02:22:22.541] All services are started 6.47418s
[Info  02:22:26.871] nereid Client Started
Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.InvalidCastException: Cannot cast from source type to destination type.
  at Gtk.TextInsertedArgs.get_Position () [0x00000] 
  at Hyena.Gui.EditableUndoAdapter`1[Gtk.Entry].OnTextInserted (System.Object o, Gtk.TextInsertedArgs args) [0x00000] 
  at Gtk.Entry.TextInsertedSignalCallback (IntPtr arg0, IntPtr arg1, Int32 arg2, System.Int32& arg3, IntPtr gch) [0x00000] 
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at Gtk.Entry.TextInsertedSignalCallback(IntPtr arg0, IntPtr arg1, Int32 arg2, Int32 ByRef arg3, IntPtr gch)
   at Gtk.Dialog.gtk_dialog_run(IntPtr )
   at Gtk.Dialog.Run()
   at Banshee.Gui.TrackEditor.TrackEditorDialog.Run(Banshee.Collection.TrackListModel model, EditorMode mode)
   at Banshee.Gui.TrackEditor.TrackEditorDialog.RunEdit(Banshee.Collection.TrackListModel model)
   at Banshee.Gui.TrackActions.OnTrackEditor(System.Object o, System.EventArgs args)
   at System.Reflection.MonoMethod.InternalInvoke(System.Object , System.Object[] , System.Exception ByRef )
   at System.Reflection.MonoMethod.Invoke(System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture)
   at System.Reflection.MethodBase.Invoke(System.Object obj, System.Object[] parameters)
   at System.Delegate.DynamicInvokeImpl(System.Object[] args)
   at System.MulticastDelegate.DynamicInvokeImpl(System.Object[] args)
   at System.Delegate.DynamicInvoke(System.Object[] args)
   at GLib.Signal.ClosureInvokedCB(System.Object o, GLib.ClosureInvokedArgs args)
   at GLib.SignalClosure.Invoke(GLib.ClosureInvokedArgs args)
   at GLib.SignalClosure.MarshalCallback(IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data)
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at Banshee.Gui.GtkBaseClient.Run()
   at Banshee.Gui.GtkBaseClient.Startup()
   at Hyena.Gui.CleanRoomStartup.Startup(Hyena.Gui.StartupInvocationHandler startup)
   at Banshee.Gui.GtkBaseClient.Startup()
   at Banshee.Gui.GtkBaseClient.Startup(System.String[] args)
   at Nereid.Client.Main(System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.Reflection.Assembly , System.String[] )
   at System.AppDomain.ExecuteAssemblyInternal(System.Reflection.Assembly a, System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.String assemblyFile, System.Security.Policy.Evidence assemblySecurity, System.String[] args)
   at System.AppDomain.ExecuteAssembly(System.String assemblyFile)
   at Booter.Booter.BootClient(System.String clientName)
   at Booter.Booter.Main()

-------------------------------------------------------------------------------

[Info  02:31:18.459] Running Banshee 1.4.1
[Warn  02:31:22.479] Cannot connect to NetworkManager - An available, working network connection will be assumed
[Info  02:31:22.492] All services are started 3.450805s
[Info  02:31:25.897] nereid Client Started
Full thread dump:

"" tid=0x0xb3ee0b90 this=0x0x378ea0:
  at (wrapper managed-to-native) System.Net.Sockets.Socket.Accept_internal (intptr,int&) <0x00004>
  at (wrapper managed-to-native) System.Net.Sockets.Socket.Accept_internal (intptr,int&) <0xffffffff>
  at System.Net.Sockets.Socket.Accept () <0x0007d>
  at Banshee.Daap.DaapProxyWebServer.ServerLoop () <0x0002d>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_void__this__ (object,intptr,intptr,intptr) <0xffffffff>

"" tid=0x0xb3fffb90 this=0x0x2f7d20:
  at (wrapper managed-to-native) Mono.Unix.Native.Syscall.read (int,intptr,ulong) <0x00004>
  at (wrapper managed-to-native) Mono.Unix.Native.Syscall.read (int,intptr,ulong) <0xffffffff>
  at Mono.Unix.Native.Syscall.read (int,void*,ulong) <0x00048>
  at Mono.Unix.UnixStream.Read (byte[],int,int) <0x00082>
  at NDesk.DBus.Connection.ReadMessage () <0x0004e>
  at NDesk.DBus.Connection.Iterate () <0x00019>
  at Mono.Zeroconf.Providers.AvahiDBus.DBusManager.IterateThread (object) <0x00055>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_void__this___object (object,intptr,intptr,intptr) <0xffffffff>

"" tid=0x0xb7e3f6e0 this=0x0x25dd0:
  at (wrapper managed-to-native) Gtk.Application.gtk_main () <0x00004>
  at (wrapper managed-to-native) Gtk.Application.gtk_main () <0xffffffff>
  at Gtk.Application.Run () <0x00007>
  at Banshee.Gui.GtkBaseClient.Run () <0x00035>
  at Banshee.Gui.GtkBaseClient.Startup () <0x00031>
  at Hyena.Gui.CleanRoomStartup.Startup (Hyena.Gui.CleanRoomStartup/StartupInvocationHandler) <0x000a2>
  at Banshee.Gui.GtkBaseClient.Startup () <0x00038>
  at Banshee.Gui.GtkBaseClient.Startup (string[]) <0x000a6>
  at Nereid.Client.Main (string[]) <0x0000a>
  at (wrapper runtime-invoke) Nereid.Client.runtime_invoke_void_string[] (object,intptr,intptr,intptr) <0xffffffff>
  at (wrapper managed-to-native) System.AppDomain.ExecuteAssembly (System.Reflection.Assembly,string[]) <0x00004>
  at (wrapper managed-to-native) System.AppDomain.ExecuteAssembly (System.Reflection.Assembly,string[]) <0xffffffff>
  at System.AppDomain.ExecuteAssemblyInternal (System.Reflection.Assembly,string[]) <0x00028>
  at System.AppDomain.ExecuteAssembly (string,System.Security.Policy.Evidence,string[]) <0x00021>
  at (wrapper remoting-invoke-with-check) System.AppDomain.ExecuteAssembly (string,System.Security.Policy.Evidence,string[]) <0xffffffff>
  at System.AppDomain.ExecuteAssembly (string) <0x00014>
  at (wrapper remoting-invoke-with-check) System.AppDomain.ExecuteAssembly (string) <0xffffffff>
  at Booter.Booter.BootClient (string) <0x00055>
  at Booter.Booter.Main () <0x00188>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_void (object,intptr,intptr,intptr) <0xffffffff>

"" tid=0x0xb5e35b90 this=0x0xc1cc0:
  at (wrapper managed-to-native) System.Threading.WaitHandle.WaitOne_internal (intptr,int,bool) <0x00004>
  at (wrapper managed-to-native) System.Threading.WaitHandle.WaitOne_internal (intptr,int,bool) <0xffffffff>
  at System.Threading.WaitHandle.WaitOne () <0x00052>
  at Hyena.Data.Sqlite.HyenaSqliteConnection.ProcessQueue () <0x000ff>
  at (wrapper runtime-invoke) System.Object.runtime_invoke_void__this__ (object,intptr,intptr,intptr) <0xffffffff>