It looks like GetFullPathName kernel.dll API func preserves trailing backslash, given in path argument, but implementation of this func in wine (files/dos_fs.c) removes it from return value (code starting at line 1300 in this file).
Info about behavior taken from http://www.clubs.psu.edu/perldoc/lib/Pod/Win32.html (I don't have authorized windows api reference and even don't want to look for it - regular wine developer can check this in seconds). Removal 3 lines of code from this file cures runtime of "Heroes of Might & Magic III" (and I don't know what too).
Regards
TreV__
-- Tadeusz Szczyrba trevor@pik-net.pl