Yep I renamed after, it was sysenv.dat
Anyway, it worked after exporting the config file from the camera where it worked to the one where it didn't. NOT RECOMMENED... lots of IP conflicts, mainly due to bonjour (Apple always screws things up on PCs...) Even turning off the bonjour service didn't help... but I managed to block one camera in the router, config the other, then swap them until the conflict was resolved. Probably would have worked (and much easier) by editing the config file.
Still, the question isn't answered... why on earth would only profiles 1 and 2 be on the dropdown list for continuous recording?
Thanks for all the input so far, hopefully we can solve this in the future. It's probably a silly firmware bug.