IM still in the 8.1 version I was going to ask if the 8.1.2 release fixed the problem, but after reading the above comment I can see i didnt.
After some experimentation i can say the problem is the rotation, I normaly use my ipad mini the upwards way locked and by using it that way the problem never shows up but, every time I unluck the rotation and rotate the screen the multigesture fails. have to work around it by pushing the notification down and up and the problem fixes until I "play" with the rotation again.
originaly tough that the problem was with apple apps because they are the ones I use the most, but after it sarted happening in third party apps I tested the rotation one and it happens almost all the time.
this really needs a fix or at least some acknowledgement from apple.