The tests in question have been unfudged with roast commit https://github.com/perl6/roast/commit/6db316eaae. (This was probably fixed with merging the 'uncurse' branch.)
The last example from the last comment (using EVAL) works as expected, too:
$ ./perl6-m -e 'say Map.new("a", 42).perl.EVAL'
Map.new((:a(42)))
I'm closing this ticket as 'resolved'.
