Look at block 317304 and block 317321.  According to blockchain.info it was solved by ghash.io, according to ghash.io they did not solve it so they aren't paying miners for it.  Those are the only 2 out of the last 100 blocks as I only just checked because someone else noticed it first.  

It could be just 2 blocks that they kept for themselves either because their software is broken (again) or because they needed an extra ~$25k for hookers and blow.  I really dont know but it does make me want to dig deeper into which blocks they have paid on and which ones they should have paid on.  If it is 2% of all blocks then there is a serious problem in not disclosing that to people, if they are going to charge a fee they need to declare it and not claim 0% pool fee.


Edit: ha! beat me to it
Edit 2: I am currently pulling blocks from blockchain.info associated with ghash.io to see what is going on.  I will also look at what IPs were used to see if one is particularly bad about it or not.  I am going to go back a couple hundred more blocks and if I dont see anything give up.  Program is running now to do all this.

Edit 3: in the last 167 blocks solved by ghash/cex pool only those 2 did not get paid out.  They still have not been at the time of this writing.