I purchased a SS Ruger 1911 Commander and have had this problem with the thumb safety returning to the fire position while in leather holsters only. In Kydex or canvas holsters it will not do that but leather belt or shoulder holsters it will remove itself from the safety position. Especially when you remove the pistol is when this happens. Why do makers replace the perfect length 1911 thumb safety with the longer ones which produce too much leverage when drawing? Three safeties are available on this firearm, thumb safety, grip safety, and brain. When drawing from a holster, you have deactivated the grip safety, the thumbs safety has been wiped down and then you only have your brain and trigger finger to rely on. It seems like no one is happy with design features on many of these 'perfect from the start' firearms and insist on improvements that cause problems down the road. I realize stronger springs and shorter safeties are available but I just thought I would point this problem out to others and be aware of it.
Having had a thumb safety roll into the engaged position, with a thumb bump while shooting the pistol, I have taken a less favorable attitude towards the 1911. And I also decided that cocked and locked was something for people whose primary use of the 1911 is fast draw games. Lots of people have found that their safety has been bumped off, when they thought it was on. And, people have found the safety on, when they thought it was off.
After studying the history of the 1911, the mode of carry prior to WW1 was a round in the chamber, hammer down, pistol in the flap holster. The users of the period expected to draw the pistol and cock the hammer. That is why WW1 era pistols have these wide hammer spurs and a very short tang on the grip safety. This pistol is the A1 configuration, the grip safety was lengthened, and the safety is a better shape.
I got this pistol because it was a deal, and it was the configuration I wanted if I ever wanted to have it as a self defense pistol. I don't trust cocked and locked, I don't trust those long safety levers, and I can load this pistol, lower the hammer (with two hands), and I can thumb cock the thing easily, without some beavertail grip safety in the way.
If you ever take a self defense class with a M1911, they teach you ride the safety, because too many times, the safety was activated to the safe position, when the user needed to take a shot. They can't do anything about the safety moving to the fire position in the holster.
In my opinion, this is the best configuration for a self defense auto pistol. No flippers, no external safeties, you shoot it double action for the first shot.