Shocking Loss of a Part from my G-Shock Watch

Bought this nice solar-powered radio-controlled (multi-band, 6!) Casio wrist watch GW-9700 about 3 month ago. Very happy about it. Touch, and needing none care at all, with the highest precision imaginable, I am putting it on everyday. But one day, I suddenly noticed that one of the 4 iconic screws one the surface is gone! What a shock (no pan meant)! I don't remember applying any shock of abnormal G any time. How can this happen!