Invalid data read from synchronously replicated hot standby

Hi,

We are getting invalid data when reading from a synchronously replicated
hot standby node in a 2-node setup. To better understand the situation, we
have created a document that provides an overview. We are hoping that
someone might be able to confirm whether or not the setup makes sense,
i.e., whether we are using PostgreSQL correctly and experiencing a bug, or
if we are using PostgreSQL incorrectly.

Link to document that contains a step-by-step description of the
situation:
https://docs.google.com/document/d/1MuX8rq1gKw_WZ-HVflqxFslvXNTRGKa77A4NHto4ue0/edit?usp=sharing

If the setup is sane (and expected to work), we will work on setting up a
minimal reproduce that avoids our complete system. We are thinking that a
scripted Ansible/Vagrant setup makes sense.

Best regards,
Martin