The way the bonus pool system is designed, you are definitely experiencing a glitch. The bonus pool is designed as a reward / incentive. A negative bonus pool would punish you for playing; there is no way this would ever be intentional. Congrats on the promotion!
Here are some links explaining the bonus pool:
I don't have any references to directly prove that a negative bonus pool is invalid, but it can be deduced from the various descriptions and observed behaviors.