There is a bunch of output at the last stage of imageBuilt, which ends with

 5,548,912   0%   22.61MB/s    0:00:00 (xfr#3, to-chk=0/24715)   
 loop deleted : /dev/loop0

This is fine interactively, but when a propellor job fails and I get email, it includes roughly 2500 similar lines, which is not so great. It would be nice if it could detect being interactive, or maybe just be quiet all the time.