Bug? Weird half bar above the menu bar when rendering with the Render window on another monitor

Blender 2.82. With multiple monitors (different DPI’s), Blender is on a monitor and the “Blender Render” window is already open on the other monitor. In this state, if I render again, a weird half bar appears above the Blender’s menu bar as you see below.

It does not go away, and if I place the mouse cursor over it, the cursor becomes a vertical resize cursor like this. When the cursor becomes like that, if I click it, the bar goes away.

This only happens when the “Blender Render” window has not been maximised. If it has been maximised, when rendering starts, it becomes “restored” window on its own (“restore” is Window’s term that is not “maximised”. If you used Windows, you should know what I mean.) and the weird half bar briefly appears on top of the Blender’s menu bar but disappears on its own instantly.

Is this a bug?

With Linux OpenSUSE Leap 15.1 I don’t have this effect.