kolossos charge + void = bug?

I was playing Kolossos on Not Perfect. At one point I got metal sonic to like 40 hp with charge so I decided to void myself during it so I could isolate metal back at my spawn but instead he died instantly?? When I tried this again with eggman during his LMS the same thing happened (he went to survivor spawn). I thought Kolossos couldn't do void damage with his abilities but does Charge not have this??