Sorry to interrupt your conversation but:

I don't use betas, final versions should simply work.

OK, I agree
I don't want to interfere in this but I'm a linux user too and, like Keet said:

I like the editors as separate tools.

and

I never had any problems with any version of the Library Editor.

Now the principal question:
which version of SH3D & FLE you use?
installed or from repository???
If is installed I (we) can help you otherwise don't expect too much from my side.
The repository versions are not in the responsibility of developer of this programs.
Until ten years ago I've have a lot of problems with the repository versions and I've never use it again.
About the categories subject I agree with you and personally I've modify it including the default library BUT again Keet has right:
you will have to do the work again after an update.
I've assumed this for my side.
Anyway it is not so often.