Shell dialogs not requested by the user may steal keyboard focus
(This is a design flaw rather than an implementation bug, so I've opted to not use the bug template)
GNOME shell is, has been, and continue to be neigh unusable when accessed remotely (via VNC, NX, ThinLinc, X2Go, etc.). The reason being that users get bombarded with system modal "Authentication required" dialogs.
We've historically seen dialogs for the color settings of the monitor, refreshing repositories, accessing smart card readers, and probably more things I've forgotten about.
In a perfect world PolKit and/or the applications would be better behaved and wouldn't spam constant authentication requests. Unfortunately that is not the current world. So GNOME popping up system modal dialogs for these requests is right now highly inappropriate.
I understand why these are system modal. But unfortunately something needs to be done. Either remove that modality, or introduce some other system that limits them.
There was a lot of work done back in the GNOME 2 days to get rid of focus stealing. Unfortunately things have regressed a lot since then, and this is one of the worst offenders.