File name being changed with strtotime

I suspect i might just be being dense or just missing something but the whole class works fine except when i don't give it a new name, in this case it changes it with strtotime. Help what am i doing wrong? The system is php 5.2 on windows.

from the manual:

$rename_file

Set this boolean if you want to (auto)rename a file (i use a timestamp as name)