Interesting. Well we need to ask IV how they'd like to handle this in Mantis. I would think, at a minimum, they'd want to add these releases to the "Product Version" field on Mantis. Obviously for bug reports to be meaningful, they need to be reported against a very specific build. This is especially so if there's going to be a lot of these builds coming out in rapid succession. Otherwise, it's going to be very difficult to ascertain when the bug is actually defeated or whether it still exists once we mix several builds and reports together.
I'm still confused by the roadmap, however. That setup heavily implied (to me anyway) that BugBash-1 would be released as a discrete build once all or most of the issues being addressed by it are ready for test. I could see a few being left off and bumped to the next release if the issue proved difficult, but 42% doesn't sound right.
Given that there's been no announcement nor video (that I saw anyway, correct?) I'm really thinking that this is just IV testing the BETA functionality on Steam. As a consequence, a few users have discovered its existence. A further consequence will be users reporting or updating bugs based on this interim release, especially if it wasn't intended to really be a release. This has already started.
Conclusion: I'm confused.