Upgrading from 3.0RC1 to 3.0RC2 does not remove admin/html.3.0RC1 (nit picking :)
 

Hi -

Just an FYI that when upgrading to 3.0RC2 from 3.0RC1 the admin/html.3.0RC1 directory is not removed.

Doesn't much matter to me, not sure it's supposed to be removed in order for the rollback stuff to work or not, but figured I'd mention it.

It is the intended behavior for the reason you mentioned already.
To remove the old version, do

lsws/admin/misc/mgr_ver.sh -d 3.0RC1