Ah, yes! It would be nice if SE would make FFXI more resilient to display changes, such as the one caused by the UAC in its default setting. Other programs using a window don't "get upset" and stop working, so why should FFXI?
Another example of when FFXI stops working and other programs continue is the update of NVIDIA graphics drivers. I could understand this might be a "bridge too far," but other windowed programs don't stop working (even other games), so why should FFXI be so touchy?
This can all be fixed by using dgVodoo2. SE's graphics engine had an "anti-cheating" feature built it, it would crash itself if it ever lost focus as the active screen. FFXI didn't allow someone to run in "windowered" mode, which is why the community wrote a special program to let FFXI run windowed known as ... Windower. Several OS's, DirectX versions and game updates later it can still be very wonky if left to it's own devices. DgVoodoo2 remediates that by usurping the games control over it's own graphics display, the game isn't even rendering to a DX8 surface anymore.
Also if dgVodoo2 seems a bit daunting to setup, then Atomos wrote a proxy library that translates FFXI from DX8 to DX9, not as good as dgVodoo2 but should fix all stability issues. Installation is just droping a DLL file into the FFXI folder (Vanilla) or POL folder (Windower).
https://forums.ashitaxi.com/viewtopic.php?f=26&t=855