installed 7.2.0 persistent (unencrypted) to 8GB USB key on 32-bit system.

Booted from key, did apt-get update && apt-get upgrade

Upgrade fails with:
Preparing to replace libc6:i386 2.17-5 (using libc6_2.17-7_i386.deb) ...
A copy of the C library was found in an unexpected directory: '/UNIONFS/lib/i386-linux-gnu/libc-2.17.so' It is not safe to upgrade the C library in this situation;
please remove that copy of the C library or get it out of
'/UNIONFS/lib/i386-linux-gnu' and try again.