Okay, I've played around with my libraries & I think I have fixed the problem for the moment.
I turned off the columns I didn't want & added a third user-defined column (currently empty). I did this to force calibre to set my preferences & want a restart. I did this for each library (restarting calibre at the prompt each time).
I then madly switched between all 3 libraries about a dozen times & it seems to be holding the column layout now.
I still don't know what was going on before but this seems to have finally *I hope* set the settings properly.
If it happens again, I look into a view manager - I presume this is a plugin?
Thanks to everyone for thinking out loud with me
