If you hit key A and quickly press a key B that will turn on preedit in SCIM (the most common input method for Linux), SCIM will catch the 'release key A' signal but the viewer won't, so key A will repeat in the viewer until you turn off SCIM and hit key A again. This happens to me on a daily basis, and most of the time key A happens to be the backspace key, so the whole line that I was typing gets "eaten", which is very frustrating... Steps to reproduce :

• type 'zzzzzzzzzzz' (don't press enter)
• turn on SCIM
• press backspace (key 'A') then 'e' (key 'B') ('e' will turn on pre-edit in SCIM). Notice the evil pac-man effect on your line onf z's. (Backspace repeats in the viewer because 'release backsapce' has been caught by SCIM)

This happens with various keys, like left or right arrows (avatar spins uncontrollably right or left) or just any letter that then fills the whole input box... Very annoying. SL viewer is the only application I use in Linux that has this bug. I believe it's because it doesn't handle inline Japanese input yet in Linux; instead SCIM pops a box in the center of the screen and input is done from there, then sent to the application when done. If I'm correct Windows version has been handling inline input since a few versions, and when it started to handle it, bug VWR-3410 appeared (and was later fixed because it was very visible to residents). Inline input is, anyway, as much wanted in Linux as it was in Windows; typing text in the middle of the screen in a tiny box is not very convenient.