Strange menu behaviour wordpress admin [duplicate]

This is an issue with google chrome, i think the devs are working on a core fix but in the mean time you can add this to your functions.php and it should do the trick:

add_action( 'admin_enqueue_scripts', 'chrome_fix' );

function chrome_fix() {

    if ( strpos( $_SERVER[ 'HTTP_USER_AGENT' ], 'Chrome' ) !== false ) {
        wp_add_inline_style( 'wp-admin', '#adminmenu { transform: translateZ(0) }' );
    }
}