Personally I feel they should be considered to be in series, as there is only one path for the current to flow. But my textbook claims they are in parallel. I'd like to hear an explanation as to why they are in parallel and not in series.
When the switch is closed they are forced to share the same voltage - this is a characteristic of being in parallel.
When the switch is open they can have different voltages,and the voltage across the switch is the sum of the two capacitor voltages - this is characteristic of being in series.