Importing and parenting mess?

I am trying to boost my movie work with some content management scripts of my own, still pretty simple design. However, the Library module seems a bit… eccentric! I used the import script taken directly from the API introduction for the Library module, but when I import anything beyond simple meshes, it screws up the models. More precisely, it screws up parenting-related issues, and only SOME of them. I imported a model with an armature, a skin mesh parented (and with vertex groups) to the armature, and a suit of armor parented part-by-part to the armature. The skin and helmet worked just fine, but nothing else was parented at all, neither to bones nor armature with vertex groups!

I have looked very hard at these odd results, but I can see no system to what will import parented and what will not. Does anyone know what I am missing here? The model works perfectly when appended manually (Shift-F1 and so on)…