Why don paired t tests work?
To ensure the correct cope is matched with the correct contrast vector, currently the contrast is automatically retrieved from the .gfeat directory after you select the cope image. Since the number of columns of the design must match the length of a contrast vector, currently you are limited to designs with the same number of columns as the original design, which prevents from calculating power for paired t tests since the number of columns is one more than the number of subjects. This will be changed soon.
