That is an interesting observation, thanks for the info..
Reagards
I have to admit is was a holster from a Chinese source, so YMMV. The velcro strap has the typical pattern you find on the back of velcro with regular bumps, see the top part of the image below. These bumps have left a black pattern on the yellow holster. The multimeter was put in the case and maybe moved around a few times, but handled gently. It wasn't carried outside, in a car or any other high vibration environment. It just sat in the case on my desk.