Alien City Question

["Aaron" <acdalton@...>]

My name is Aaron Dalton and I run a free play-by-web boardgame site
called Super Duper Games (http://superdupergames.org).  I am in the
process of implementing Alien City (and other Piecepack games) and
have a question regarding the Alien City rules.  The rule in question
is this:

5. The lot containing the suit icon in the corner of a tile may not be
built on until after all other legally buildable lots on that tile
have been built on.

Combined with rules 3 and 4, this one is giving me a headache.  Can
somebody give me an example of a situation where building on the suit
icon is permissible if there are only 1 or 2 existing structures on
the tile?  I am hoping that the phrase "on that tile" means that legal
moves elsewhere on the board aren't taken into account.

I appreciate your time.
Aaron