Here's a new development: the "Blackberry icon equals download button" test no longer works. Specifically, the absence of that icon doesn't mean the absence of a download button.
Example:
Striking Mars - no Blackberry icon, but it shows up fine (DRM-free EPUB 2, download button) in my library. Meanwhile,
Hot Blood XI has the same icons, also shows up as a DRM-free EPUB in my library when I add the sample, but does not have the download button. In fact, downloading the sample through the Kobo desktop app and examining it directly reveals that it's also an EPUB 2 book.
So - two books with the same profile. Both EPUB v2, both without DRM, both without the Blackberry icon. One gets the download button and one does not.
This is just a mess.