When I am cleaning up my cards, I frequently repeat the action of clicking to open a card, then clicking "Archive". Trello recently added a "Get Power-Ups" advertisement above the "Move/Copy/Watch/Archive" buttons that loads just slowly enough that the "Archive" button moves down just before I click it, and I end up clicking "Copy" instead.
Once a user interface is displayed, it is NOT OK to move the buttons around into different places! If you are loading something dynamically, either put it at the bottom of the screen so it does not affect the layout of the rest of the user interface when it loads, or reserve a fixed amount of space for it in your layout.
I'd love to open a bug report on this,