As the bug relates to an out-of-date mesh, there are some simple workarounds to the problem, all of which involve forcing the mesh to be regenerated. The two easiest workarounds are:
- Turn the mesh on under View Preferences. When the mesh is on, it will be regenerated automatically.
- Save the file after deleting the region. The mesh is regenerated when the file is saved. (It is not necessary to close and re-open the file, simply saving it is enough.)