First, thank you for this great "swiss knife" plugin.
I'm on WP Multi-site with WordPress MU Domain Mapping plugin (http://wordpress.org/extend/plugins/wordpress-mu-domain-mapping/)
When I click the button in the visual editor on a mapped domain I get the login screen in the box where I should get the snippets.
The buttons on the html editor are working fine.
When I'm on a blog that is not mapped everything work as expected.
Any idea of how to fix that weird behavior ?