In GDI Campaign mission 8 there is a constant power level 0, which can't be changed with any number of conyards/power plants. I think it isn't supposed to be that way. EDIT 3: Strangely enough, the power level did start to work properly after selling a power plant, so this mission is playable anyway.
EDIT: There is also an issue with tiberium not regrowing from a tiberium riparius tree after all tiberium has been harvested from that specific tiberium field, so that the tiberium riparius tree just stands there without any tiberium around it like forever. [look at edit 2]
Another thing worth mentioning is the fact, that harvesters do not recalculate their waypoints after a structure has been built in their way, resulting in the harvester standing or turning around in one spot near the refinery, not moving towards the tiberium field.
EDIT 2: Didn't notice there is a cash limit to each tiberium riparius... btw, does it have to be that way, or is it done intentionally, to limit player's resources, to make him rely more on offensive strategies?