Well, maybe they fixed this issue in TLR model, but I'm sure that on mine (CFN) if you switch from cloudy to sunny, you'll get the very same aperture. I saw this shooting in B mode with no film and the back open. But you know these are particular cameras, maybe it's just a defect of mine, even if I read of other people having the same problem.
I do not have an Holga, but this issue have been mentionned many time. If I understood correctly, the hole in the plastic is smaller than the hole in the aperture plate.