I think it's just the high standard deviation the 1024 diff involves.
My rig posts a share every minute / MH/s.
So sometimes you can have more than 5 minutes without a share.
It's still showing correct values in middlecoin graphs.
Nope, it's not that.
This is what happens to me. It looks like nothing is happening, except hashing, and then a string of accepted shares will come in after a while.