Android- Nexus 7, and Samsung (unknown model - out of the office)
Collector 10.3 - using esri hosted maps.
There is 1 named user, me, also an administrator on the online side (shouldn't matter). Same user who downloaded the map.
I found it interesting that even with a complete data delete from the app settings and with an uninstall and re-install of the app that the downloaded maps were still present. I am guessing it is a hanging-lock type of situation but would still like to get all the data off the devices to free up memory.