plib, are you claiming special knowledge of what happened? Speculating? Admitting to something?
This is my speculation--it could have been on the Kobo end, or the publishers. Publishers monkey with pricing fairly regularly--adjusting for specials, changes in currency--all sorts of things. Kobo does their thing. Unless a Kobo staffer tells us what happened, we will never know for sure (barring the possibility that plib has been fooling around, of course
).