This is a problem for beta 2a.

I don't know what you did, but you seem to have over-compensated when fixing the problem mentioned in this post.
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Suffice to say, sometimes when you build a power plant, it isn't built, instead leaving an open tile after it is finished building. This same problem also occurs when building one of a kind stuctures such as starports.

I'll try to setup a good save that demonstrates this problem, and then e-mail it to support.

P.S.
Since we are on the subject, there is another problem I've been forgeting to report. Sometimes late in the game, if you were to destroy a starport, it cannot be replaced. It doesn't show up as a buildable structure thus creating a planet that can't produce ships. This occurs regardless of the method of used to destroy it, such as an invasion tactic, or being decommissioned.