So you're sitting a province, but playing just one province. Every now and then a link you click - and kingdom/province links are by far the most common - will switch you between provinces. This results in numerous instances where players attack with the wrong province, for instance.

This happens as well when not sitting. Some links simply won't work, and when you look at the link you'll see it's because it's a sit link. There may be no way to access that particular page without editing the link.

I use the classic theme, with umunk enabled. However I'm pretty sure the other themes are affected too.