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.