About the subject of exporting MATs out, then making new libraries without the 'bloat' of stuff that's not supposed to be there and should have been deleted....

That is, you delete an item from a library but it only deletes the thumbnail, not the actual library item itself.

Does the new version 5.5 of Bryce suffer from the same bug?

BTW, doesn't that bug exist for all the libraries not just the material presets?

It's a chore to carefully de-bloat my libraries, mainly the ones that get deletions a lot. To counter that I created various temp libraries so I could lessen the number of libraries to de-bloat, mainly when I'm testing and experimenting with MATs. - Works for me. :-)