I'm running Beta 2 on Windows 7 x64, emulation set to Brief. When I'm in a diff of two files, I occasionally will modify one of the files directly within the diff window. Alt-W is my Brief key binding to save the file, but it doesn't work in Diffzilla view. But I sometimes reflexively use it anyway rather than Alt-1 (save file 1) to save.
In VS20, Alt-W just does nothing. In VS21 beta 2, it acts as a destructive backspace, deleting the character to the left of the cursor. In a normal window I also have Alt-? (Alt-Shift-/) bound to what-is. I tried that in the diff view to try to find what Alt-W was bound to, but it too did a destructive backspace. Undo does at least work.