How to reproduce:
  Input the following with ibus libpinyin:
  * meili -> ������ works
  * li -> ���: writes a space (0x20) instead
  * xiaoli -> ������: writes a space instead
  * lichang -> ������ works
  * li -> ���
  * lizheng -> ������: writes a space instead
  * limian -> ������ works
  * li -> ���: writes a space instead
  * liyuan -> ������: writes a space instead

This list is surely not exhaustive. And in all cases I need to switch back to
another language and back to libpinyin method to be able to input chinese
characters again.

Those are working properly with ibus-googlepinyin input method.