What are the techniques for controlling what happens when you drag a Trello card?

Question

Dragging Trello cards duplicates instead of moving them. Why? How can I control this?

Am seeing that when I drag a card to another position within the board, rather than moving the card, it creates a duplicate of it when I drag it to the bottom of a list. If I drag it instead so some location within a list, rather than the cards moving out of the way to make room for it, the card become an attachment inside one of the cards.

This only happens when I am using Trello within the browser (Safari) on my desktop computer. When working within the Trello app on my iPad, I can drag cards and they simply move, they do not duplicate. I would prefer this behavior when working within the browser. How can I accomplish this?

Added gory details:

When I drag a card, a green plus sign appears over it, and text appears listing the label category of the card, a number, the title of the card, and then "Drop files to upload. Too many app...".

Tom Vanderlinden · Accepted Answer

So in Safari I logged out of and then closed the Trello pages I had open. Then went to Preferences > Privacy > Manage Website Data, and then searched on "Trello". There were 5 different caches. I selected them all, then chose "Remove" and "Done".

Then went back to the Trello site and logged back in. Problem gone, can drag cards anywhere within a board, no issue.