When you click and drag to move spells and items on the actionbars, the instant you click to drag, the spell casts or the item is used, which is really bad, triggering long cooldowns, using potions etc.

This is because you have cast on downpress enabled, and sadly this is just the default behavior when that happens. No workaround except disabling cast on down.

I have no gui to do this currently, though. I'll consider this a feature request and put it on my todo list. I have no ETA currently.