Were you prompted twice for a description?
Nope, only once. However, I pressed "OK for remaining" on the download dialog. Could that be part of the problem? Hang on, I have a theory. Let me try a quick experiment...
Well then, what I find is that when I do not use %P in the destination folder mask then everything works fine (i.e. all the correct folders are created). Furthermore, if I use %P and click "OK" for each picture as it downloads (not "OK for remaining") then feature works correctly as well.
Although it works under these circumstances I think it's a bit crippled, and would prefer one of the following behaviors when "OK fo remaining" is clicked:
(1) Use the same description but create a folder for each unique date in the photo set.
(2) Prompt for a description for each unique date in the photo set, and of course create a folder for each date. According to your question quoted above, this is what I think you believe the behavior should be.