It also happens because you press on an item, it gets bigger, and then it moves because other things had to move to make space, and then when you let go, you've now got your mouse over a folder instead of the original item you pressed on.

It can be solved in several ways. Besides being more careful you can:

1. Change the Tree "Selected Thumbnail Size" to be the same as the Thumbnail Size 

or

2. Display items in the Item List Panel, instead of in the tree.

From the day I started building that UI, I thought it was weird to have the items be mixed with the folders, and to have the item change size when you touch it. But that's what the SM User Experience team wanted.

Later I added the option to turn that off and to use a separate panel to show the folder contents. That is the only way I use it - with multiple panels. Because of that, I never have the accidental drag and drop problem.

---

Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)