Hello,
I'm pretty sure it's my fault but never happened so there's a very little chance this is an issue :)
When I rename the folder into bulk_user_admin the plugin disappears from the list in admin section.
If I rename it with any other name the plugin becomes visible again with error message "This plugin is invalid: This plugin's directory must be renamed to "bulk_user_admin" to match the ID in its manifest."
I also checked docs ( http://learn.elgg.org/en/stable/appendix/faqs.html#plugin-cannot-start-and-has-been-deactivated-or-this-plugin-is-invalid ) but everything looks correct...
Cheers