Sometimes those screw-heads are asymmetrical in that when they rotate they seem closer on one side. Not sure if that is the possibility here, but make sure everything stays stationary, in its place & try to extract the screw. Keep in the floorplate in readiness in its battery position and doesn't rise giving the impression that the screw isn't backing out.

The Topic name is novel......

Cheers,

Raimey
rse