Thanks Mike,When you say it's not working, what do you mean exactly?
As rydiger said, the store's purchase logic will go to extremes to ensure that you pay the lowest possible price. To qualify for a Superbundle, you have to pay the bundle price for the minimum number of titles to qualify (two, in the case of the Ghostbusters bundle). So, let's say that you had a disc-to-digital offer for each of the four movies. You would end up just paying the disc-to-digital price, since it's lower.
If you have a disc-to-digital offer for one movie, and you selected that movie plus one other, you might end up paying slightly more than the disc-to-digital price for the one movie, but by doing so, you qualify for the bundle and pay much less overall.
See the thread rydiger linked to for more. Also, this reminds me that I don't know if we actually posted the explainer document I wrote. It was awaiting review.
I was ordering 2 of the Ghostbusters bundle, one was D2D and the other was regular price. My D2D upgrade price was $4.92, when I purchased the bundle price was $6.99 each total of $13.98.