I was working on a mesh to create a new UV map for it. The UV unwrapping showed me some places in which the topology was awkward (tris in places that they could be quads), so I popped back over to edit mode, and fixed it by dissolving the bad edges and creating good ones. I neither created nor destroyed the existing vertices in this process.
Now my UV map has some rather large holes where there should be new edges. Is there a way to ask the UV editor to update where it has its edges placed?