XP boost application past 2 hours stacking

When I went to apply my XP boosts and had used enough for 3 hours (2 60-minute boosts, 1 30-minute boost, and 2 15-minute boosts), the timer did not go past 2 hours, not stacking any additional boosters once two hours had been reached. Not a huge issue, but given that they aren't exactly common, it was a bit disappointing.