Reverse thrust transition to idle...

Hi!Whenever I retard from reverse to idle thrust I notice a jump forward in the plane as if I've put positive thrust.. I taught It was strange for this to occur but presumed it was correct, util I've read that this may nor occur in real life.There is a simple test. Standing still in a runway just aply full reverse and then put in idle and see what happens!Before any one ask's, I have all the controlers properly calibrated INCLUDING a neutral zone...Jos