No obvious reason why there might be a moldng issue, but the hole for the tri-wing screw through the plastic battery tab closest to the hard drive would not align at all with the threaded hole beneath in the unibody metal, There is little play in the position of the battery for realignment, so I had to ream that hole through the plastic laterally with a small drill bit in order to reinstall that screw.

Otherwise installation was easy with the iFixit battery and tool kit.

No plastic tab on either the stock battery or the new one from iFixit