Do you really need the REAL filename?
Or would "Gegner_Weißer Drachenreiter_stehen_png" do for "Gegner_Weißer Drachenreiter_stehen.png"?
Try error(mypan->bmap->link.name); (once the panel mypan is created of course)

ALSO: Just tested paanel behind entities. Panel must be negative layer AND sky_color must = 0,0,0