A new build of the Xperia keyboard with version number 5.6.D.1.28 is currently rolling out to Sony Xperia S owners. The update mainly brings “software performance improvements“, with no other noticeable changes. We are not aware of it hitting other handsets, but if it has, let us know in the comments below.
Update: It also appears to be released for the Xperia P.
Thanks Trevor and xJokerz!