BuddyPress.org

@zomex – You might want to try this in your theme’s functions.php:
remove_action( 'init', 'bp_core_add_admin_bar_css' );

if ( !is_admin() )
add_action( 'init', 'bp_core_add_admin_bar_css' );

Untested, but give it a shot.

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Actually, based on your report, it’s hard to give a definitive answer. What exactly is breaking in the admin…

@zomex ignore the query string it’s a version string appended when the style sheet is added to the output of the page and is simply a method used to force refresh of browser cache , it’s appended to the file after the fact and no file actually exists physically with a query string, just edit the […]

@zomex – If you’re trying to override the adminbar CSS on the subblog, create a file called:
/wp-content/themes/_YOURTHEME_/_inc/css/adminbar.css

And copy the styles from bp-default’s adminbar.css. Then you can customize the styles to your heart’s content.