Having reinstated the draw slit mode, it turns out that the draw trace does not work on these slits; the reason is that the draw traces work on slits with tag=loaded, that is assigned to the slits taken from the region files, but not to those created on the fly.
Having reinstated the draw slit mode, it turns out that the draw trace does not work on these slits; the reason is that the draw traces work on slits with tag=loaded, that is assigned to the slits taken from the region files, but not to those created on the fly.