[gameplay bug] chogath ult. incorrect

When using chogaths ult as described it's supposed to give a half cool down if you use it on a minion, such as jungle creeps. But, about 1/3 of the time while eating even normal lane minions it does not give the half cd, it quickly flashes the half cd then continues for the full time. I love playing chogath but when his ult is inaccessible for almost an extra 40 seconds for unexpected crucial moments it becomes quite bothersome.

I'd love it if someone could look into this and try sort it out, I have a bad PC so I can't take videos or screenies easily in game but I think this describes it pretty simply.

Thanks,

Mr leprachaun (Jason)