Comment 2 for bug 810942

Sorry for very late reply...

I might not understand your problem, but if the 'backspace' means typing C-h, please try the following setting:

(setq ibus-clear-preedit-when-unexpected-event t)

This option changes the behavior when preedit exits by typing a key not handled by IBus. If the value is non-nil, preedit text will be cleared. If nil, it will remain.

Thanks for your report.