Since it's now possible to import the same thing twice, I added a test to S11-modules/import.t with the following commit: https://github.com/perl6/roast/commit/02a309ec81 and I'm closing the ticket.
[perl #118231] Importing the same thing twice shouldn't bomb
Christian Bartolomaeus via RT Thu, 16 Oct 2014 00:01:55 -0700
- [perl #118231] Importing the same thing twic... via RT
- [perl #118231] Importing the same thing... Christian Bartolomaeus via RT