Well... I would take a sharp razor, or knife, and CUT IT OFF! The strap is unnecessary unless required by some department policy for LEO's, if the holster is well designed.
20-30 years ago, most every holster came with a strap, and we were stuck with them. I moved away from straps years ago... They get in the way. Most don't allow for one-handed re-holstering, and in many cases, the snap provides a false sense of security.
Many who get holsters with a thumb break feel the need to prevent the cocked hammer from failing, and falling on a live round.
Sadly, the misinformed fail to realize what is actually required for the hammer to fall on a 1911... At least one that has been verified for safe operation.
The thumb safety would have to be off, the grip safety depressed, and the trigger pulled (on a S80). FWIW, the thumb strap would not prevent the Firing Pin from moving if enough enertia occurred to get it moving toward a primer.
Out in the field, on horseback, or maybe an ATV, I could see a reason for having one, but for most people, I see no real value, and again, with a properly designed holster, they are not necessary.
Lastly, I'm betting that you tried to snap over the uncocked hammer, although a new, un-broke-in holster could be tighter than normal.
