I have carried a Government Model 1911 in a Ted Blocker LFI-1 rig for well over 20 years and I have found the safety disengaged perhaps 4 times. Being self employed, I get to go active in the field, and play office boy too.
My safety has never dis-engaged while shuffling papers in the office. Always in the field working or playing hard. For this reason, I trust my holster and check it at times.
If your safety dis-engages on its own on your 1911 pattern pistol, take a look at what you were doing and keep it in perspective. Chances are good that you do not need a new holster after all. just slow down a little.