See, this was the Bills plan all along...
The Bills, in all their wisdom, knew in training camp that Merriman wasn't ready to go. But they couldn't stash him anywhere or let him take up a roster spot. So the Bills brass said "Hey, Shawne, we're gonna cut you. But don't you go worrying, when you are all healed up in a month, we're gonna sign you back."
Shawne, being the loyal player he is, goes along with this great plan. He even plays it up on twitter saying things like "I'm not a defensive end in this league." When, we as fans all know, Merriman was a stud DE in college. Then Merriman, gets healthy and boom, he's back.
It's all part of the plan...