There is an entry in the Change Log ...
[2010-03-13] REL: VERSION 2.46 (for Windows XP/2003/Vista/2008/7)
[2010-03-10] FIX: blanks before extension part in file names were automatically removed at Replace actions for _FILENAME.
Points your discussion post to this fact?
If so, then there might be something to report relating to Mp3tag 2.46c.
Having a filebasename of "test .mp3" and using action "Replace" to replace the string part "test" with nothing, then the resulting filebasename from within Mp3tag is " .mp3" and so stored into the filesystem.
WinAmp can add this file to it's playlist.
The underlying filesystem (NTFS) can hold this filename, but the file cannot be accessed at the commandline, for example for renaming.
Windows explorer can rename this file, but removes automatically leading space characters.
Filerootnames with trailing space characters are always allowed.
Conclusion:
Per definitionem it is not allowed to design a filename starting with a space character.
Therefore a filename like " .mp3" is an illegal filename.
Mp3tag should avoid to create such filename.
DD.20100928.1045.CEST