oil change question
It is not uncommon for either the check valve in the oil pump block or the balance shaft to seep what was in the frame into the crankcase. This could be from a poorly machined check valve seat, loose tolerances or maybe debris hanging something open slightly or any combination thereof. This is why you only refill with about 1.5 quarts of oil after a full drain because if more gets into the sump it can get above the piston and cause hydro lock. Can happen quickly but generally more after a long time sitting in the heat... sometimes it just comes and goes. Generally not believed to be detrimental to engine life however if it keeps you awake at night nobody will stop you from draining the sump and pouring it back into the frame.