The Milt Sparks Summer Special does not have that shield that comes up over the thumb safety. However.... in my experience, the shield doesn't matter regarding the safety coming off. If the safety is fitted where it has a positive feel when it snaps on and off, it will stay on. That shield is to keep the safety from poking you in the side.
The SS 2 and I think all the other holsters from Milt Sparks have the shield. I use a VM 2 and an EX and like the shield just for comfort.
If I'm carrying my Government model, it's in an old Summer Special and I'll eventually remember why I like the others better.
The only safety issues I've ever run across are with ambi safeties. I have smacked the gun into something and knocked the safety off. This wasn't done walking around the house and tapping furniture, it's more like crawling around under cars or moving lumber.
Even so, that still leaves several safeties on - grip, finger, brain.