EDIT : I was correct.You did send two merits one after the another.There is no glitch,lock the thread.
It has been reported many times already. Refreshing the page will double send Merits and it is also possible to double-click the send button and do the same.
Is the case same here ? Maybe I'm missing on the 'reported many' part,mind linking me to one of those threads where this glitch is actively being discussed ? I thought the OP sent one merit after the other and just couldn't see it due to page refreshing stuff.Anyway,I don't know if this has been discussed before but I found something interesting while fiddling with the merit input box.
https://bitcointalk.org/index.php?topic=3292443.msg34351320#msg34351320