How exactly did you play it with counting the hits carried over from the previous round of combat?
Was it like this?
round 1: score 5 hits (against 3hit unit) - remove 1 stands, 2 wounds remain. 5 to combat resolution.
round 2: score 2 hits (against the same unit) - remove 1 stand, 1 wound remains, 4 to combat resolution.
Doing it like that, wouldn't you count the 2 hits (which got carried over from the first round) twice?