Editing of preferences causes parsing error and prevents application of some preferences

[confluence]

I have recently noticed that whenever I edit any preference through the frontend dialog, I get this error in the Firefox console:

XML Parsing Error: not well-formed
Location: http://192.168.0.98:3003/api/database/preferences
Line Number 1, Column 1:

Additionally, while some preferences are applied as normal (e.g. turning event logging on and off), some (e.g. overlay settings) have no effect. They are saved correctly, and are applied the next time I open CARTA.

I have reproduced this on Ubuntu Focal using both the carta and carta-beta packages, after clearing my user directory so that a brand new one is created (so the issue is not an old preferences file). I have also reproduced this in the latest dev backend + frontend built from source.

In Chromium I do not see any error output in the browser console, but I see the same symptoms when I try to change the overlay settings.

[kswang1029]

Might be helpful if you can attached example json files (a working normally one and an edited problematic one).

[confluence]

@kswang1029 this isn't being caused by a corrupted file -- it happens even when I remove the user directory and a new one is created.

[veggiesaurus]

may be related to not setting content type to JSON