I carry concealed whenever I legally can, and it's mostly a 1911 in condition 1 carried IWB in a Milt Sparks Versa Max 2 holster. I've never had the safety come off.
First, I make sure that any 1911 I might carry has a very positive "on-safe."
Second, the holsters I use are leather and have a sweat shield between my body and the gun. The sweat shield has become slightly scored by the safety in the engaged position, and that also helps.
Formerly known as fiddletown