Abilty ranks bug?

Megatronus83

So today I mixed out some of my abilities on the siphoning tree so I switch them out for some assassination abilities. For some reason thru maxed out to rank 4 after about an hour so I decided to switch them out again. I logged off and came back on and I noticed the abilities I recently used before I logged off changed back to rank 1. My question is does abilities that u don't use revert back to rank 1 or did I experience some sort of bug?