Here's how I can reproduce it:

1) delete both the config dir and the cache dir
2) import a single album
3) mark all the songs and open the metadata editor
4) check the "album artist" box and try to enter anything in the text field
5) Banshee crashes

I suppose at this point it's trying to offer me some autocompletion (find-as-you-type) magic but instead I get this:

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] in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Libraries/Hyena.Gui/Hyena.Gui/EditableUndoAdapter.cs:112 
  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) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui.TrackEditor/TrackEditorDialog.cs:line 659
   at Banshee.Gui.TrackEditor.TrackEditorDialog.RunEdit(Banshee.Collection.TrackListModel model) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui.TrackEditor/TrackEditorDialog.cs:line 581
   at Banshee.Gui.TrackActions.OnTrackEditor(System.Object o, System.EventArgs args) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui/TrackActions.cs:line 309
   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() in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 144
   at Banshee.Gui.GtkBaseClient.Startup() in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 77
   at Hyena.Gui.CleanRoomStartup.Startup(Hyena.Gui.StartupInvocationHandler startup) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Libraries/Hyena.Gui/Hyena.Gui/CleanRoomStartup.cs:line 54
   at Banshee.Gui.GtkBaseClient.Startup() in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 72
   at Banshee.Gui.GtkBaseClient.Startup(System.String[] args) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Core/Banshee.ThickClient/Banshee.Gui/GtkBaseClient.cs:line 62
   at Nereid.Client.Main(System.String[] args) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Clients/Nereid/Nereid/Client.cs:line 48
   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) in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Clients/Booter/Booter/Entry.cs:line 106
   at Booter.Booter.Main() in /home/users/builder/rpm/BUILD/banshee-1-1.4.1/src/Clients/Booter/Booter/Entry.cs:line 100