More of an annoyance bug than a game breaker, but -> With a race that has the Colonizers ability (first building on a new colony is free)...
If you select a project like Economic stimulus, the next turn you see that this project is displayed as Rushed in the manufacturing queue. If you select a new building, no production gets added to the new building, because each turn it thinks you have rush bought economic stimulus, thus no production gets actually added anywhere. (You can still select a different building after you cancel the rush of the project first, still getting your new free building so no big deal.)
Steps to recreate this:
Colonize a planet, select Economic Stimulus as your first building/project.
Go to next turn.
Look at colony screen... Economic Stimulus listed as rushed.