Hi Steve,
Those do indeed look strange and very similar considering they were taken using very different light sources which should have produced very different looking flats. Are these images raw or are they the master flat after processing in ISIS? If so do the raws show the same effect? Here is a flat from my setup last night (ATK428) using the halogen lamp in the calibration module. (reduced in size)
As far as I can recall flats taken with a halogen lamp plus white sheet over front of the scope as a diffuser before I had the calibration module produced a similar flat.
Robin