[RC20] invalid byte sequence for encoding "UTF8"

Upgrading Docker for Windows from RC16 to RC20.

With RC16 my application (connecting to a docker container with Posgres 9.5.3) was running fine.
Same application with no changes fails on RC20 with error " invalid byte sequence for encoding “UTF8”. "

Rolling back to RC16 -> everything works fine again

Maybe related to this ?