[Q] XT1034 adb backup won't work topic

Trying to back up some data from my XT1034 (stock unrooted 4.4.4). When I run, for example, "adb backup -f shopping.ab org.openintents.shopping" to back up a single app... the phone shows the confirmation dialog with two buttons on the bottom: "do not back up" or "back up my data". So far this is what I expect... but when I try to push "back up my data" the phone does not respond. Only the "do not back up" button works. When I push it both buttons are greyed out, the computer stops waiting for the phone to respond, and of course nothing is backed up. Am I missing something? Or has Moto blocked this?