Re-ordering files within collections doesn't stick

I’m pretty sure this is a new problem.

When I reorder files within a collection, using control-up or control-down, the files move okay and are visible when clicked. But if I then go to a different collection, or to the binder, and come back, those files that I moved up or down are back where they were before I moved them. This happens on several collections. And I don’t think it was happening a few days ago. Have I inadvertently changed some setting that I don’t know about?

I just discovered that if I drag and drop the files the reordering becomes permanent, even though the control-up or down changes disappear when I leave the collection.

I suspect this difference might be a deliberate feature, designed perhaps to allow users to experiment with different data flows without losing the order we started from, and then to drag and drop when satisfied. But if so, I think that should be mentioned in the manual

And that still leaves a problem. If I’ve fiddled around with the order of a couple of dozen files, using the control-arrow commands, how can I do the drag and drop to finalize it without losing my new sequence. It’s late at night my time and I’m getting woozy and have probably missed something obvious, so somebody please jump in and give me a pleasant morning.