AppStore MAS Installment:
the MAS update under El Capitan here indicates for v.1.9.2 a 379 MB download. It starts the download of 379 MB and after that when it reaches the state to install, during installation, shortly before finishing installing it says "wait" and then reinitiates a new download of 729 MB. - So one always downloads 379 MB and then continously another additionally 729 MB here (aka 379 + 729 MB all in all)! - The same happens for the Designer installment. - BTW, I've seen this same behavior also previously for the v1.9.1 Mac AppStore updates!
So the overall behavior here is always, MAS starts the update by downloading first a lower overall file size of 379MB and installs it. But shortly before finishing the 379 MB installment, it autoresets and reinitiates a new huger 729 MB download which it then installs!