Gravity, strange torque

Anyone who has spent an overnight at our place knows that we have a sheet metal shower stall in our one full bathroom that seems to have been lifted from a Korean War era Quonset hut.  It's great virtue - the reason why it's still there (other than inertia and money) is that it is the ultimate in anti-low-flow plumbing: big honkin' streams of shower water, which I adore.  (Allow me to digress, and say why we love our friend Ms. Higgins: because when we embarrassedly say how we've been meaning for 14 years to rip out the old bathroom, she says, Why!?  Why would you want to change anything about it!?)

Anywho, this is about the latch on the stall, nicely illustrated over there on the left.  See the top screw?  Every couple of days I notice it's loosening, and I screw it back in with my thumb.  (Right thumb.  Always the right thumb.)  What's that all about?  How's it loosening?  Why?  What's the strange gravity and torque? 

The only thing I can come up with is that the torrential waterflow creates a coriolis effect so strong that it wrenches the screw loose. 

That's my story, and I'm sticking to it.