bp doesn’t really have a blog id in the member theme. So the problem is relative to what? bp references locations relative to the root blog, blog id 1 when it has to. This is to locate bp resources.
/* The domain for the root of the site where the main blog resides */
$bp->root_domain = bp_core_get_root_domain();
Whenever I refer to anything in bp I use absolute references. Relative references are just asking for trouble. IMHO.