For the short blocks, if two blocks are found inside the same share processing window, the second block is basically lumped in with the first one. I do it this way because I do not want to punish slower miners. If we counted the actual shares for a fast block, only the fastest miners would end up getting paid and the slower miners would get screwed. The faster the pool gets, the more prominent this would become and I did not want to screw anyone out of BTC. So now ultra-short blocks are basically counted by the amount of shares you submitted for the previous block, making it fair for everyone.
Any blocks found within ~2 minutes or each other will be counted together. That should give the slower miners enough time to submit at least a few shares towards a block, unless they are mining with CPUs or something.
You'll notice on 0 share blocks your payout is almost exactly the same as the previous block, it's like getting a block for free!
Brokk: What do you want to know about the glbse shares? I'm not sure I follow your statement or question?