Unable to Recreate a library with Multiple Collections

My library exists on LT with books belonging to 3 different Collections.

Then, I created a Full Library Excel export.
I then used power edit to remove all books from the library.
I then rebuilt the library using the full export file in CSV format.

All books came back with proper tags but only the Your Library Collection.
The Excel export file has all of the proper Collections in comma separated text just like for tags.

What can I do to obtain the unimported Collections?

I did eventually insert the proper Collections by editing the Full export file and making 2 extra copies, each of which had only one of the two missing collections.
This worked for me, but it should be totally unnecessary and a system fix to this seems available.
Since multiple tags are properly dealt with on import, why not multiple collections?
Is there something I have missed?

>1 JFB87: Nothing can be done. This is a feature. There is no way to export the library, edit it, then reupload it. Never has been.

>3 gilroy: OK, so I will just content myself with the solution I devised.

Alas, this is a long-requested RSI (recommended site improvement) that I would love to see happen (complete export-import loop), but we don't offer it at this time: https://www.librarything.com/topic/219575. Please follow that thread for any updates, and I'm sorry for the inconvenience.

>1 JFB87: How very disappointing! And all those hours or work you can't get back. I learned the same lesson a couple of days ago with an experiment with only 12 titles. And it took me the better part of an hour to sort the mess.