My questions are: do I need to treat my internal drag and drops the same way as my external ones? Is there an external and an internal DnD working simultaneously? Is there a way to know which instance a DnD is coming from?
Sorry, bad reply in previous post.
No, you can treat internal and external as you wish fit.
Internals are just another format. The only difference is that internal does not move data to the clipboard (keeps them in local memory), so it does not need to define external format.