EDIT: This is now fixed on ember-table master, as of https://github.com/Addepar/ember-table/commit/9de978d8e6299a9429881b2ec212dcb79c49722f.
This is an issue with Ember Table and has been filed in the issue tracker there. Until there's a better solution (and we welcome pull requests!), your best option is probably a workaround like you have now.
By the way, I've broken both of your JS Bins by updating ember table. Sorry about that. Now that we have versioning, this shouldn't happen in the future. To update your examples, just paste in the dependencies from the new starter kit.
More discussion can be found here or here in the Ember Table issues. I have another JS Bin which illustrates the issue: http://emberjs.jsbin.com/nedac/3/edit.