Sometimes can't use attack move when Rapid Firecannon is at 100 stacks

Not sure if anybody else is having a similar issue but sometimes my attack move (press 'A' then left click) won't have my champion auto attack once its reached 100 stacks. I noticed this during one of my games as Miss Fortune earlier. If I hit a 100 stacks and then tried to attack move, I would walk to where I selected but never attacked anything even when it was in range. I tested it out a bit more and noticed that if I was already in combat and I got 100 stacks while in combat then tried to attack move it was fine though. But once I was out of combat and then walked up to a minion wave or camp with 100 stacks and tried to attack move, my champion wouldn't attack unless I right clicked. However, if I didn't have 100 stacks and I tried to attack move after I had been out of combat, then I would attack as expected. Again, not sure if anyone else is having an issue but I thought that this was a weird bug.