Authentication window not triggered in 5.1.20 (worked in 5.1.7)

[MartinSusky]

Version 5.1.20: Separate authentication window is not triggered, making it impossible to authenticate with a different account than the one connected to Windows.
Version 5.1.7: Authentication window was triggered correctly and login with a different account worked as expected.

[bgribaudo]

Encountered this today, as well.