[perl #75640] calling nextsame in an proto causes a Null PMC Access

[via RT]

# New Ticket Created by  Moritz Lenz 
# Please include the string:  [perl #75640]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=75640 >


proto sub a($x) is export { say "in proto"; nextsame }
sub a(Str $x) { say "Str $x" };
sub a(Int $x) { say "Int $x" };

a([]);

causes

in proto
Null PMC access in clone()
  in 'a' at line 1
  in main program body at line 5:Foo.pm

Note that even when the nextsame() dispatch should succeed (in case the
proto is exported, and on calls a(3) from a calling module) the same
error occurs