Comment 9 for bug 238309

From a technical point of view, it seems that some keystrokes get "eaten" by the application or some library instead of being buffered for transmission to the IME.
Candidates to look into would be: oo.o, libx11 and fcitx, IMHO.

To find the source of the problem we would need to know
 a) if this problem also appears with other IMEs or only with fcitx
 b) if this can be reproduced in other applications or only in oo.o

As I'm not a fast typer, I cannot test this. Any fast typing native speaker out there who can test this?