Steps to reproduce:

1. Create new project
2. In scene view, press right click and while holding it, move mouse to the edge of the viewport
3. While still holding right mouse button, left-click on the "line" which could be used to resize scene view
4. Move mouse to scene view and try to perform any mouse action, for example, pan the scene view
5. Notice that scene view is unresponsive

Reproduced with: 5.1.4f1, 5.2.4f1, 5.3.4p6, 5.4.0b18