i tried what you said and it really removes bmap in this case
BMAP* bmap;
PANEL* panel = pan_create("bmap = testa_bilde.bmp", 1);
bmap = panel.bmap;

I then added this bmap to other panel and after removing first panel second left without bmap. So in this case it removes bmap too;

But in case i added bmap after creating;
PANEL* panel = pan_create("bmap = NULL", 1);
panel.bmap = bmap;
Removing panel didnt remove bmap.

So now i know it, but it will make all tracking harded for deleted and undeleted things.