System Information
Operating system: Darwin-20.1.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 570 OpenGL Engine ATI Technologies Inc. 4.1 ATI-4.0.47

Blender Version
Broken: version: 2.90.1, branch: master, commit date: 2020-09-23 06:43, hash: rB3e85bb34d0d7
Worked: (newest version of Blender that worked as expected)

Short description of error
The preference called 'Region Overlap' works properly in 3D viewport but does not work in other Editors like Curve Editor or Dope Sheet Editor.

Exact steps for others to reproduce the error
Turn on Region Overlap from Blender Preferences>>Interface>>Editors
Now in Blender's 3D viewport, press 'N' ot 'T'. The Region overlap work well (i.e. it keeps the viewport zoom / scale etc. intact)
Now try pressing 'N' in e.g. the curve editor. It shrinks the editor. While it should keep the zoom / scale of the editor intact. The 'N' panel should get drawn on top / overlaying the editor.
This is very important specially while using the 'Synch visible range'.