[perl #84438] Initializing a lexical array in a subroutine body later leads to wrong illegal redeclaration error

[via RT]

# New Ticket Created by  Moritz Lenz 
# Please include the string:  [perl #84438]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=84438 >


$ cat bug.pl
sub foo() {
    my @b = ();
}
foo( my @x = 1);

$ ./perl6 bug.pl
===SORRY!===
Redeclaration of symbol @x at line 4, near " = 1);\n"

This error goes away if I do any of the following:
 * don't initliaze @b
 * don't initialize @a
 * remove the parenthesis around the sub call