Before Firebird 2.1 config parameter TempDirectories allows to specify temp directory size to use by Firebird.
I.e. entry in directory list might contain number separated by space, for example :

TempDirectories = c:\xxx 100; d:\yyy; d:\zzz 10000;

Therefore when this list was parsed rightmost space character was searched for and chars from this position up to the end of entry was removed (it was supposed that it is a number).

Starting from Firebird 2.1 this logic was abandoned but removal of characters from rightmost space to the end of directory entry was left in code