amumu bug report

So, when i play amumu, red team want to kill me and when i dead, i push my r. But the bug is my r didn't go into the cd, i don't know is it a bug. But if everytime it's happened, full ap amumu each team fight all need to do is go into enemy time push r，bring 5% dead time less，tp back push r again. It's really op. I hope it will be fixed.