Reproduced, and logged a bug for it
SQL Developer QA Team
Ah, took a bit, but this only happens when (and in certain, as yet undetermined circumstances, as soon as) the Editor (data viewer) is placed in the left ("Navigator") dock. This may also happen in the mirror image case, but I have not tried it.
The bad news is that this is not a loop in the classic sense, but more a game of hot potato with crossed event notifications. "Who" needs to keep quite and under what circumstances is still a mystery.
The good news is that this behavior is easy to avoid. Arranging the editors as desired in the center dock area works fine. I would suggest starting with the connections still expanded to get a feel for the difference in how the dock target outline indications look between "left half of center" and "on top of connections". This can also be done via the context menus creating tab groups in the "editor" area.
SQL Developer Team