NEC 3520 - Strange or smart read speed?

My 3520 unit acts strangely: if I insert a disc for the first time it starts reading at 3.5x and goes up to 13x; if I eject the media and reinsert it again it reads at 6.5x and goes up to 16x (full speed); and finally if I eject and reinsert it runs it quielty starting at 1x (!). The firmware is 1UE - does anybody here notice this behaviour? Or Iā€™m just seeing things :confused: