I believe it started after the Lil Pri anime (where she did not play Cinderella, Yuuka did) and extended well past gen 2 joining since there were several clips of Akari trying to get Kanon's goat by stealing her gimmick.
I know it doesn't count toward Oricon or anything... but I actually really like this single, so I bought a copy today along with Kikkawa's and C-ute's last singles. J=J's last one will have to wait for their next release
Kanon does indeed look a bit off in that picture. Or she was just too occupied with torturing Rinapu's elbow, who in turn doesn't seem to notice and looks remarkably radiant in the pic.