Why does your neutered male cat hump blankets?

i had my male cat neutered last thursday...as a matter of fact, today he began humping again (blankets etc)..neutering just removes the reproductive nerve but sometimes the cat just is used to these behaviors and continues..my male cat is approx 2 1/2 according to the vet...he began humping shortly after i found him and let hin live w/me..he was already maybe a year old when i found him..the vet informed me that sometimes these behaviors will continue but over time may stop.