That can happend if the two rivets that hold the shutter holder are a bit too loose. You can make sure they are set properly by making a "pincer" with your fingers and pressing them in after unfolding the camera...
One of my Iskra was doing that, and I ended up using a plier to /gently/ pre-set the rivet. Be VERY gentle, if you don't you might not be able to fold it again!