Game stole a birthday booster?

So I had used a birthday booster on one of my characters for WvW and EoD mastery grinding, but then I remembered that I had another character that hadn't been to Cantha yet, so I decided to hop on them and use a 2-hour experience booster to power through some masteries. As far as I'm aware, booster effects are character-specific as I had used a birthday booster in the past and was able to play on other characters with no issues. However, upon logging back into the character today, the birthday booster is no longer there despite only being logged into them for an hour tops which means I should still have 23 hours left

Does using a booster on another character overwrite boosters on others or is there something else going on that I'm not aware of?