why this are legal:
<?php echo "comment1"; # comment1 ?>
<?php echo "comment2"; // comment2 ?>
<? echo "comment3"; # comment3 ?>
<? echo "comment4"; // comment4 ?>

but the PHP parser won't accept these?

<% echo "comment1"; # comment1 %>
<% echo "comment2"; // comment2 %>

i think this is a lack in the parser code which controls
the # and // comment style. Am I right? Can be fixed?

Of course a workaround is:

<% echo "comment1"; # comment1
%>
<% echo "comment2"; // comment2
%>

sorry for my bad english (i'm italian).

hope this is useful

best regards

Antonio Bonifati