On every new branch I create, and since the past 3 or 4 versions, when I attempt to create a pull request from SourceTree it often prompts me with:

I don't even have to change the settings, I just need to open them once and save again (they are already correct).

The issue goes away until the next system restart (Windows), then it rears its ugly head again, so I guess it must be related to some temporary storage.