Re: Discrepancy in query output

​Apparently st_distance() is non-deterministic in its output of float representations.  Its seems likely (though I'm by no means fluent on floating-point concerns) to be a problem specific to the implementation of that function and thus better asked on a PostGIS list.  You should identify the "extra" row and see if you can include it in a self-contained query that demonstrates occasionally returning false for the condition when normally it returns true.

David J.