Yes, the note in perlsyn advising against trying to use this construct:

       NOTE: The behaviour of a "my" statement modified with a statement
       modifier conditional or loop construct (e.g. "my $x if ...") is
       undefined.  The value of the "my" variable may be "undef", any
       previously assigned value, or possibly anything else.  Don't rely on
       it.  Future versions of perl might do something different from the
       version of perl you try it out on.  Here be dragons.