Possible incompatibility with this hardware? Have you tried with a different (plain and simple) keyboard and mouse - that'd be the first thing I'd try.
I have the same problem with the latest version of the BIOS, i.e. 0097. Moving the mouse over a selectable item triggers teh action as if I had pressed the mouse button. When switching to Classic mode, it is very difficult to save and exit as the confirmation dialog appears momentarily and disappears as if the Esc key has been pressed immediately.
I am using a wired keyboard and a wireless Microsoft Optical Mouse 3000 and will try with a wired mouse.
Well, once I replaced the wireless mouse with a wired optical mouse my problems went away. So, the moral of this story, avoid using a wireless mouse, especially the Microsoft Optical Mouse 3000, in the BIOS screens.