As a status update: This seems to be specific to the REPL. Executing the code
from the command line throws a typed exception X::Export::NameClash (output is
identical for perl6-m and perl6-j):
$ perl6-p -e 'constant %a is export = 5 => 5; constant %a is export = 5 => 5'
===SORRY!=== Error while
# New Ticket Created by Dagur
# Please include the string: [perl #118505]
# in the subject line of all future correspondence about this issue.
# https://rt.perl.org:443/rt3/Ticket/Display.html?id=118505 >
> constant %a is export = 5 => 5
5 => 5
> constant %a is export = 5 => 5
Null PMC access