Qt4 : disappearing non-English characters

I’m developing a flash-card application to help myself learn the Chinese
language. I’m using ruby1.8 with Qt4 on an xubuntu system.

At first, everything is rendered correctly, but after displaying a
certain number of flash cards, the non-English characters in the updated
in the GUI are not rendered to the screen. For example, if there is
word, such as, “bXn”, where X is a non-English character, then it is
in the GUI as “bn”, i.e. the middle, non-English, character is totally

For reference, I dump the words to a command-line terminal, and the
non-English words/characters are displayed correctly.

The problem is consistent in that for a given input flash-card database
file, the non-English characters disappear at a certain number of
flash-cards (the
flash-cards are displayed randomly, so it is not associated with
specific cards).

The larger the flash-card database, the sooner the non-English
characters disappear. The flash-card database is a simple UTF-8 plain
text file.

I’m guessing that it is a memory-related problem in Qt or the
Qt/Ruby-binding, but am unsure how to debug it.

Any suggestions would be greatly appreciated.