Cannot register private customer on frontend.

Prereq.: Ibexa Commerce 3.3.2-dev. (following https://github.com/ibexa/engineering/wiki/Installation-via-Flex)

Steps:

1. On frontend got to /register/private
2. Fill all mandatory fields, use a password with 4 lower case letters and one digit at the end.
3. Click Register.

Actual result: User is not registered, error occurs in UI "User object not given", exception occurs in silver.eshop.log:

Could not create and/or login eZ publish user: Content Fields did not validate
Error while processing the form data: User object not given

Expected result: User is created and ready for activation.

Remarks: Does not occur on v2.5.7 & v3.2.6. Explained below by Mikołaj why it could not occur.