Operating system: Windows-10-10.0.18362-SP0 64 Bits
Graphics card: GeForce RTX 2070 SUPER/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 445.87
Broken: version: 2.90 (sub 0), branch: master, commit date: 2020-04-20 18:51, hash: rB55a2682348df
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-03-12 05:06, hash: rB375c7dc4caf4
Worked: (newest version of Blender that worked as expected)
Short description of error
After you open the file explorer and the first click you do will select an object behind the window if there is any. Annoying if you use selected objects to export. Seems to only happen if you use a shortcut to export to any file type. Couldn't reproduce with selecting file -> export -> any file type.
Edit: If there is no objects behind where you click you will deselect everything.
Exact steps for others to reproduce the error
With default scene. Short cut some export file type. File -> export -> filetype -> assign shortcut. hit the shortcut and if you click in the file explorer window where the default cube is you will select it.