Steps to reproduce:
1. Type any single character with Kotoeri.
2. Press backspace.
Results: The character is selected instead of being deleted.
I think that this is a pretty recent regression.
Created attachment 16872 [details]
test case for platform/mac/editing/input
I'm not sure if this test actually works, but it should hopefully be close.
Backspace works in TOT, I think I broke this and then fixed it in r27009.
Sorry - I was indeed using an old build.
However, there is another problem with the same steps to reproduce, filed bug 15714.