Install plugins with FTP upload, virtual subdomain, bad base dir?

Hi anybody!
I have problem with install plugins with FTP module in WP.

Everything show as OK, but plugin directory is bad. I have subdomain

sub.something.com – this is virtual subdomain from mod_rewrite

dirs are

/www/something.com/something.com
/www/something.com/sub.something.com – here is WP installation

After install – WP say everything OK – but one thing is bad.
Upload is in bad directory – plugin I can found in
/www/something.com/something.com/plugins
no in /www/something.com/sub.something.com/plugins

Is here some way to fix it automatticaly or I can must edit config and basedir of ftp? Why is here this bug?

Thank you !

Pavel