I’ve tested on both Mac (Catalina) and Manjaro Linux.
I seem to be able to reorder things in a drag-and-drop list (e.g., a tag pill) as long as I start my drag from the right of the text. If I grab the text, then sometimes I get an an HTML dump showing up in the list. But I can’t make it happen consistently. Like Stan, I was also not able to find a problem with dragging in the open list specifically, but I
do have the horizontal/vertical problem on both machines.
I tested again and this time I was able to copy a tiddler between wikis by dragging and dropping into a different tab. I’d thought I wasn’t able to do that before either, but evidently that was wrong.