It stays as the Professional edition when you uninstall because the license files stay in your Program Files/Spybot 2 folder,most likely so it will remain as the Professional(or Home) Edition when people uninstall to upgrade when newer versions are released.
This is a known bug,and there is a workaround here:
http://forums.spybot.info/showthread...l=1#post457317
The bug is in the free edition as well,so if/when you reinstall,you might like to stick with the professional edition,as that shouldn't effect whether the bug is there or not.