Summary of Bug Report
Dragging a panel from the tab header (e.g. "Call Tree" text) allows to re-position the panels, but after re-positioning, the UI doesn't do update/repaint, so the re-positioned panel may be left displaying a blank content, and other panels may show partial content, based on their previous size.
Response and Plan
Yep, annoying but hardly lethal. I've had a look but it's not an easy fix. This will be fixed but with lower priority, as the impact-to-effort ratio is not great.
Any action that causes update/repaint of the panel will re-compute the size, which will then display the panel correctly, so for example you can just scroll around in Call Tree panel to get it display properly.