System Information
Operating system: Windows-10-10.0.18362 64 Bits

Blender Version
Broken: rBedffb0e9b19d (2.81 development version, master)
Worked: rBedffb0e9b19d^

Short description of error
[missing button Open or Import, or export, link , append, in new popup window when is on full screen mode]

when is not maximalized it back again

Exact steps for others to reproduce the error
[open new file, import, export, and maximaize pop up widnow to fool screen)]