Travelynx.pm: Document the real cause of sched_arr-isa-DateTime bug

			)->then(

				sub {

					my ($traininfo) = @_;

                  # FIXME when a station appears several times in a route

                  # (e.g. Frankfurt Flughafen on some nightly connections), this

                  # method chain sets the same timing reference on each stop,

                  # causing murder and mayhem later on (e.g. in get_user_status)

					if ( not $traininfo or $traininfo->{error} ) {

						$self->app->log->debug("traininfo error");

						return Mojo::Promise->reject("traininfo error");

				for my $station (@route_after) {

					if ( @{$station} > 1 ) {

						my $times = $station->[1];

                   # TODO this is a workaround.

                   # A station may be present several times in @route_after

                   # (e.g. Frankfurt Flughafen at some nightly connections).

                   # At the moment, there's a bug causing the time ref of

                   # each stop to be the same -> ensure that it is not converted

                   # to DateTime twice.

						# Note: $station->[1]{sched_arr} may already have been

						# converted to a DateTime object in $station->[1] is

						# $dep_info. This can happen when a station is present

						# several times in a train's route, e.g. for Frankfurt

						# Flughafen in some nightly connections.

						my $times = $station->[1];

						if ( $times->{sched_arr}

							and ref( $times->{sched_arr} ) ne 'DateTime' )

						{