fb-adb shell gives confusing error message

[tcmulcahy]

$ fb-adb shell ls
fb-adb shell: adb error: failed to copy '/tmp/fb-adb-ovCQRP' to '/data/local/tmp/fb-adb.bc60fb8f679fc9509d17': Permission denied

I'm seeing this on a Nexus 5 running Lollipop userdebug build. It happens when the phone is partially off. When I touch the power button I see a battern icon, with an animation indicating it is charging. Surprisingly, "adb shell" works. But fb-adb shell gives the above error message.

Turn on the device and everything works again. So it's not terribly high pri.