OK. Both 11/21 and 11/22 FRED builds crash on start. Furthermore, they maintain an application process that refuses to shut down. The Debug also complained about missing explosion LODs, but the weapon_expl.tbl entry (TBP BTW) indicates that there's only one LOD for the weapons being referenced.
OK, it turned out that the missing explosion LOD stuff were actual errors, which I've since fixed, but that still hasn't prevented FRED from crashing and refusing to release its memory block from the process window.