(gameplay) lissandra ult bug

I ulted twice in a teamfight. i ulted kassadin when i got caught and i e'd away over a wall. Then i checked my cooldowns and i noticed that my ult was up. Instantly after the ult ended on kassadin i got it back. Then i tried it out and i ulted their garen. Sadly i don't have a clip about it because my lolreplay is not working atm. I only got a screenshot of the aftergame. It has only happened to me once. I don't know how to reproduce it but i hope that you can fix it :)