tiny_mce_before_init filter is not fired for users with Author role
|Reported by:||paulmackinlay||Owned by:|
http://www.designzzz.com/how-to-stop-wordpress-editor-from-removing-iframe-and-embed-code/ explains how to change wordpress so that you can embed an iframe in a post without tiny MCE removing it.
This works fine if you are logged in to wordpress as an administrator. It has no effect when you login to wordpress as an author.
I guess that the tiny_mce_before_init filter is not fired unless the user has an administrator role.