Argh! right.
lpe-knot for groups does not work :-(

One bug is not directly in lpe-knot, but in the initialisation of the array parameter in the case of groups (which is wrong in some cases).

But trying to reopen the svg source, I see more than this about groups and lpe:
when an lpe is applied to a group, the behaviour is strange: it seems the effect is definitely applied to the members each time it is run (try bend for instance).
In particular, if you try to node-edit the objects, they only show up in theire deformed version... where we'd like to have the original object.

Playing with this a little generally let inkscape crash.
I'm not sure, but I think the behaviour was correct when I did the lpe-knot test file... :-(

Cheers, jfb.