Okay, so that’s weird.
I’ve played with the file now and yes, if you select the very last shape key from the IPO list, its properties are empty (in the 2Mb test file) but it shows a Key Y: 7.80. Each preceding key shows a reducing Key Y value less 0.1 (7.8, 7.7, 7.6, 7.5…).
In a simple test, if you reduce each of these Key Y values to 0.1, you get one to one mapping. As best as I can tell, the Key Y value just determines a channel’s position in the basis IPO window (the blue lines for each key when “basis” is selected). In the old RVK system these lines used to pile on top of each other unless you changed frames between key settings (not pleasant).
Although Theeth mentioned the Key Y value, I wan’t sure what he meant but I just started deleting shapes (except the jawopen one) until finally, when all had been deleted, the 7.80 changed! Then I went back and did it again but in random order until it changed again. And from there is was look and see until the Key Y value reared its ugly head on the last shape in the list.
From the outside, this looks like an unintentional side-effect of separating the basis lines (whatever they’re really called) for each key but since I couldn’t code my way out of a wet paper bag, I’ll leave that for others to adjudicate.
Edit: As I recall, in the old system the blue lines were useful for selecting an RVK for editing. They seem a little redundant now that we can easily select and edit shape keys. So I wonder, do they have a practical use that requires visibility?
Also, I should add that since this is not a bug, as such, and that there is now some clear indication of where this 7.8 number comes from I think it’s safe to say “That’s the number it stays at until it changes” 