So my contract ended with this company, and I was still in their payroll system I guess. I don't know what they were using, but the company had 16 annual paid holidays. Every paid holiday, I would get a kickback for a full day worth of work at $28/hour. It was very clear that somebody had effed up, but I didn't feel as though I was under any obligation to correct their mistake. The company was (and still is) fairly large, so I doubt anyone would have ever noticed.
I actually entered a new contract with this company rather recently for a 24-month term (after 4.5 years of getting these paid holidays). It looks like my PTO in their payroll system has been accumulating the entire time I've been gone, because I have just over 9 weeks of paid time off available to me in their system. Now, using that PTO may be a little too obvious, but that holiday pay that I was misallocated is just far too sweet to pass up.
Edit: I'll update this post if I get caught.