Technically it’s not a glitch if you have to reload it, but I’ll try to explain this at my best.
First off, the servers already know you were a moderator. And once you post a new reply or comment, it still knows that, it pretty much just saves it until you reload or come back to that page to put the “M” next to your username.
As I said in the first sentence, it technically isn’t a glitch. It’s more of a server delay.