Casino tribal casinos one thing I find strange

whats up people...
i was just wondering has anybody noticed (tribal casinos are concerned) that if you bring your own money to the casino you seem to win? but as soon as you cash out a voucher and play with their money that comes out of their cash back machines (95% of the time) you seem to not win anything. its almost as if hypothetically speaking of course that the casinos knows that the money your using was won or was from a cash out voucher. so they take it all back. when i come there with my own money i win 95% of the time and when that money is gone and i cash out the vouchers i dont seem to win at all (there are exceptions of course) like 95% of the time. what is stopping a casino from recording the serial numbers on the bills to know if the money came from the casino? they regulate themselves whos to stop them? its just a program and easy enough to do. I just find it strange is all. I've asked a couple people. has anybody experienced the same thing?