I think Phil has hit the nail on the head, I think you may have the larger clamps, whch are for a number 9 blade and upwards and not many of us use blades that course. I think the clamp with the smaller gap is the 0.5. I have quite a few of these and I use number 7 blades and smaller, a lot smaller and never had a problem with the clamps not holding the blade.
Another cause of the blade coming adrift from the clamp is oil and grease within the clamp and also oil on the blades, you can clean the clamps by taking the alen blt out from the right hand side and running a piece of abrasive through the clamp a few times. If you do this be careful you don't lose the little silver inset at the end of the bolt and make sure it is clean when you put it back. Please let us know the outsome to your problem.