What are some apps that do proper ('negotiated') Drag-n-Drop?

Question relevant to this inspector app I’m working on: what determines where a given BMessage is routed?

I ask because the final B_MIME_DATA reply I’m receiving, doesn’t go where I’d expect - it’s being routed to my BApplication, instead of the window/thread that sent the message it’s replying to. Is there something about that type of message that can only be sent to an app, and never a window?

It’s not a problem per se, I can route it where I ultimately need it. Mainly I just want to verify that I’m not doing something wrong to cause that.