About Cleaning up junk (garbage collector)

Lets say a scene started off around 70-80mb, it loaded a swf in, and by removing the event listener and setting objects to null and numbers to 0 before unloading the swf,
and went back to the original scene, the memory stack up till like 80mb++,
and every time I repeats the same process the memory goes up higher,
is that normal? or its a memory leaking issue?