Annie bug with Tibbers

It happened to me playing yesterday on a an ARAM, every time I tried to ult instead of summoning it would add an 8 second longer cool down.

One time afterwards it did the same thing but instead brought the summon damage through but didn't actually summon and just added 8 seconds again.

Afterwards I tried it again and couldn't get it to do it again, wasn't sure if it was a one time thing or I was just unlucky.