When building a new base, there where 2 'tiles' next to the entrance that could not be used to build on. These 2 tiles looked greyer and 'rocky'-like. (dead spot).
That's no fun if you have only 1 more tile you can build on...
maybe this bug was alreday reported, but i didn't find it anywhere ...
i had the same probleme before, so it didn't just happened once.
as an example: it is also shown in this movie, at around 4 minutes of playing time.
http://www.youtube.com/watch?v=cAg1lmotHFA&feature=relmfu