If a file is catched in the upload filter (i.e. has " " in it's name and these are replaced automatically with "_"), at the same time I18N
chars in the file name (like for instance "ø" and "Ø") is changed into UTF8 encoding, i.e. "Ã¸". At the same time they are uploaded as "UnknownUser", not as actual user.
Just for completeness: There is no problems with I18N
chars as long as the filter is not triggered.
P.S.: I know I18N
chars in filenames is bad practice
Darn, this was on an ancient install (DEVELOP/9159), it's fixed in 4.0.2 / TWiki4.