Smashwords?

I've gotten several requests for my three stories "Cutman" "All About Eden" and "Footjob" to be made available in non-Kindle format. Several readers suggested Smashwords, so I checked it out. Seems simple enough. But as usual, there's one little fiddly bit that doesn't quite make sense.

So, question for the hivemind: If you've already published something on Amazon, you can't make it available in Kindle format on Smashwords, right? Seems logical, but when you publish there's a big warning beside the Kindle/mobi option that says (in all caps no less) DO NOT deselect the Kindle format.

What gives? Anyone else had to make this choice? Of course there's nothing about it in the FAQ, no tech support and I haven't gotten any response on the Facebook discussion page. I'm not planning to do the fancy premium catalog option, I just want to make these stories available to any readers who might want to check them out. You know, keep it simple.