I've noticed on the latest version of firmware (not sure on earlier versions) if you apply a tick in the enable remote management box and deselect a protocol the port gets still 'reserved' and an inbound port redirection will fail.
The way round this is to put http and https onto non-standard ports, eg:
Remote management ticked, http unticked but on port 80 and an http redirection is set up on the box it will fail. Alter http management to port 81 (still unchecked) and the port redirection now works.
Would it be an idea either to put a warning notice on the web interface or code it so if a protocol is unchecked it is available for redirecting.
Cheers,
Rob