5060 - underwater housing mode

Ive been using a 5060 underwater. The camera has a mode where you can tell the camera it is being used in an underwater housing. When this is selected what does the camera do differnetly from when it's not selected?

What I found is that even if the camera is set to external flash, the internal flash still fires (probably a preflash). When I turn on the underwater housing setting, all flash is external only, and no internal camera flash fires.

Joe