Strange Result of Datetime::diff

Hi, 

I'd expect the following script: 

<?php

$date1 = new DateTime('2017-03-01');
$date2 = new DateTime('2017-04-02');

$diff = $date1->diff($date2);

echo "{$diff->m} months and {$diff->d} days.";
?>

would print "1 months and 0 days.". But instead it prints "1 months and 3 days." (see https://3v4l.org/RMuUZ).
What is the reason for this behaviour?

Thanks in advance and best regards
Christian
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