Bug in DateTime::Format::ICal parse_recurrence?

I'm not sure if this is me being dumb or whether it's an actual bug.

Given this code

use strict;
use DateTime;
use DateTime::Format::ICal;

my $hour  = shift || 0;
my $start = DateTime->new(year => 2008, month => 3, day => 1);
   $start->set( hour => 18 ) if $hour;
my $recur = DateTime::Format::ICal->parse_recurrence(
                recurrence => "FREQ=WEEKLY;BYDAY=MO;UNTIL=20080331",
                dtstart => $start
);



my $iter = $recur->iterator;
while ( my $dt = $iter->next) {
        print "  ".$dt->ymd."\n";
};


I would expect to get the 5 mondays in March on the 3rd, 10th, 17th, 
24th and 31st and if you run it without passing a command line argument 
then that's what you get.

However, if you run it as ./script 1 then you don't get the final 
occurrence on the 31st.

I'm guessing it's the mismatch between the precision of the UNTIL and 
the $start - should something (either DateTime::Format::ICal, 
DateTime::Event::ICal or my code) truncate the $start to the same 
precision as the UNTIL?

Thanks,

Simon