It does happen to me once in a while.  Usually it is when I am pushing too much on an old blade that has dulled.  It's the wanting to stretch out the life of the blade instead of changing it. 

When I first change the blade I check it a few time to make sure it still is tight.  I find that the blade will slip out of the bottom holder slightly.  I reposition it and keep cutting.

Make sure it is well into the bottom holder.