BigRedConsulting: I wasn't aware of the Multiple Windows/One Window setting. I've always been in Multiple Window mode. However, I tried your suggestion as given and it fixed the problem. Now the column widths are staying exactly as I resize them. So why did this trick work, and how are users supposed to know this trick, and why doesn't QB support know about this trick?

Maybe it's not a trick at all. Would resizing have worked properly if I had been running in One Window mode all along? (I've now changed to One Window mode as that's what I should have been using anyway. Resizing is working.)

Thanks very much for this fix. This will save a ton of time and frustration daily. I hope everyone else who has commented on this Item List column resizing problem sees your post and follows your suggestion to get it fixed.