Spam. Robots cracking the graphic code?

So far, I hve been preventing any spam with Coffelius Graphic Code Generator (introduced in the Wiki: Tackling comment Spam). Humans need to copy the code they see in the graphic to a new field in comments
Since three days, Texas holdem seems to be able to crack the graphic code in some messages. No idea yet why. Others have not come through yet.
I’ll explore it further. If any of you has an idea, let me know