with current git head f8ec49175f4767

open attached files:
meld left right
copy dh_python2 from right to left
save
undo (ctrl z)
save
=> crash:

Traceback (most recent call last):

+ Trace 228064

debugger run:
> /home/jtaylor/tmp/meld/meld/undo.py(182)checkpoint()
    181         end = self.next_redo
--> 182         while end < len(self.actions) and self.actions[end + 1].buffer != buf:
    183             end += 1

ipdb> p self.actions
[<meld.undo.GroupAction object at 0x319e9d0>]
ipdb> p len(self.actions)
1
ipdb> p end
0

fixes seems simple:
-        while end < len(self.actions) and self.actions[end + 1].buffer != buf:
+        while end < (len(self.actions) - 1) and self.actions[end + 1].buffer != buf: