Team ult indicator not syncing correctly

The indicator located above the player frames down in the right corner of the UI that shows if team ultimates are ready or not seems to have some syncing issues.

I just played an ARAM match as Rumble where I got chewed out by my team for not using my ultimate to secure a kill during a chase. The reason I didn't use it was quite simply because it still had 8 seconds left on its cooldown as we were chasing, but the indicator was apparently showing as green to my team so they would hear none of that.

The ult really was on cooldown though, both my Shadowplay capture of the match and the replay confirm that, so there must be something wrong with the synchronization of the indicator.