Looks like spaz has uncovered a bug in B::Deparse.

% perl -le 'print "a" =~ /a' -e '/x'
1
% perl -MO=Deparse -le 'print "a" =~ /a' -e '/x'
-e syntax OK
 
print 'a' =~ /a\n/x;

% perl -le 'print "a" =~ /a\n/x'

%
[download]

Oops!

(I'm taking advantage of the implicit newline for -e.)