Could it be that they are not going "round" the entire track, rather that it is going only part way, back and forth? If you look at the Disney map, from DTD it goes past the front gates of DL, then back up towards the Matterhorn, meandering around the submarine ride, Autopia, etc., stops at Tomorrowland, goes through DCA and again ends at DTD. Then from DTD goes past the front gates of DL then back up to meander through Tomorrowland, finally stopping back again at that station.
I would expect that they aren't doing that anymore because of the construction on the new Nemo attraction. Therefore, just going "forward and reverse" on that southern strip of track. I would expect that there is only one train running back and forth.
At my last trip we only rode the monorail from Tomorrowland to DTD, so not sure if the above is true, but seems likely.