[MasterGunner01]

John Browning equipped the M1911 with four safeties:
1) Thumb safety that locks the hammer in the cocked position on a loaded chamber (Condition ONE).
2) Grip safety that must be pushed in (gripped by firing hand) to release the hammer when the thumb safety is OFF and hammer cocked.
3) Half cock safety that prevents an accidental discharge when the hammer is cocked or lowered. This is NOT a carry safety.
4) Disconnector safety that prevents an out of battery firing if the slide and barrel are not locked-up.

If the safety went from locked to off, I would check for a set slide stop/thumb safety spring. Also, check thumb safety and detent for wear. Replace spring, detent, or thumb safety as required. Under usual handling, there should be effort required to move the safety of a cocked M1911 from ON to OFF (or vice versa). It will not happen by just brushing against it; it has to be a conscious act.

[Cboldt]

I wonder if the thumb safety is one of those oversize, enhanced ones, too. I agree with you, certainly for the standard thumb safety. No way it should get to the firing position without a deliberate act.