This is an issue that exists also in Pro 5.x
When a dialogue box is open, or when editing an element, if you click and drag from within the field / text / code editor and release your click over the preview pane, a new element is selected / the focus changes / the dialogue box closes.
This can be quite infuriating when editing element controls, especially those containing Dynamic Content, as when clicking and dragging to select the content, I often drag just beyond the inspector pane, and releasing the click over any element in the preview seems to register as an actual click, thereby changing my element selection, changing the inspector context, and requiring a click back to where I was working.
Hopefully this video shows the issue clearly: