I hate posted this bug for 6.03 already complete with screenshots and the likes...
not seen it in 6.12 afaik... not happend to me anyways
with 6.03 it happend sometimes... but the reason why was not clear. it wasn't with very busy channels or anything... just a few windows that were affected from time to time.
text that spread more lines was just cut in half (first line of the buffer)
really weird bug it was