While in Edit Mode, selecting the geometry in the 3D viewport doesn't cause the same selected geometry to show up in the UV Editor window.
It's only when I begin modifying the selected UVs that the UV Editor updates. At this point I can cancel the transform and the newly selected faces remain.
This problem is happening to only one object in the scene. The object was working fine previously, so I must have enabled/disabled something unintentionally.
I've checked that 'View > Update Automatically' is enabled. Given that it's happening to only this object however, I don't think the problem is with a UV Editor setting. But I don't know what object-specific setting would cause this behaviour.
Any help would be welcome, cheers.