[shatner]

The new UW spell Ride the Currents won't allow mages to travel to a friendly fort under siege in an UW province. Is that intentional? Conversely, you can use that spell to travel to an enemy fort that your forces are besieging.

I haven't checked if the larger version of that spell (Traverse the Sea) will or won't allow you into a friendly, besieged fort, but it certainly bears investigation.