The notification 'A folder cannot be dropped into itself' is too easy to trigger accidentally when trying to open the folder and accidentally movind the mouse a few pixels. If I don't keep the mouse perfectly still while clicking on the folder, this notification appears. I've lost count of the number of times I have done this. I can see that the notification could be useful when dropping a folder from one side of split view to the other, or to another tab, but when the folder has only been dragged a few pixels the warning is unhelpful and distracting. In this case, I think the notification should not be shown. It would be nice if Dolphin opened the folder as intended, but just suppressing the notification would make this less annoying.
Thanks for the report. If you have the feeling that drags get triggered to easily, just increase the minimum distance to start a drag in the System Settings (Hardware/Input Devices -> Mouse -> Advanced). See bug 307747 for more information.
Well that certainly helps me (I didn't realise that could be configured), but my point really was that the notification is not helpful when I have not really dragged the folder onto anything, I have just dragged it a short distance and let go of it. I would expect that to just cancel the drag operation rather than attempt to move the folder into itself. I still think you should consider this, though your tip about the drag start distance should make me see it less often.
Maybe you didn't get my point: if you have moved the mouse pointer by more than the "Drag start distance" (which is a global setting that we are supposed to respect), then the drag *has started*. There is no arguing about it, and it's not Dolphin's business to decide that the user did not actually want to drag and cancel it if the "Drag start distance" was exceeded only by a small amount.