I used the following steps to reproduce the issue (as outlined in the upstream bug report):
1. Start a project and begin a new window.
2. Add a checkbutton.
3. Modify the text of the "Label:" field for the checkbutton, starting in the middle of the existing text.
4. Witness the cursor jumps to the right after each key stroke
Testing with glade-3 version 3.4.2-0ubuntu2 I was able to reproduce the issue. Started typing in the middle of the existing text of the "Label:" field for the checkbutton. The cursor jumps to the end of the text box after each key stroke.
Testing with glade-3 version 3.4.5-0ubuntu1 from hardy-proposed. This issue is fixed.
I'd however like to make a note that it appears the actual package that is responsible for this fix is really libgladeui-1-7 version 3.4.5-0ubuntu1. glade-3 has a dependency on libgladeui-1-7 being installed but it is not strict on which version of libgladeui-1-7 needs to be installed. As a result it could be that glade-3 version 3.4.2-0ubuntu2 was installed which also had installed libgladeui-1-7 version 3.4.2-0ubuntu2. If you then pulled in updates from hardy-proposed and installed glade-3 version 3.4.5-0ubuntu1, libgladeui-1-7 isn't automatically updated to the necessary version 3.4.5-0ubuntu1 and the bug here will still exist. I even tested keeping the older glade-3 version 3.4.2-0ubuntu2 installed and updated libgladeui-1-7 to version 3.4.5-0ubuntu1 and indeed the bug was resolved. I hope that makes sense.