Upgrade redundant pair memory tag issue

I have problem when upgrading our redundant gateways. I lose the information in memory tags.
I created a simple client that shows values of different datatypes during upgrade of a gateway pair. The buttons are just a lazy way for me to change all values at once. I follow the recomended routine for upgrading a redundant pair.

Values before failover in 8.0.12

Values after failover
As expected, no change

Upgrade master gateway to 8.0.13
Now I have two active servers, and client is still connected to the backup gateway.

I now change the values in the tags.

Now I am lost. How will I get the backup gateway memory tag values synchronized with master?
To me it looks like they won’t talk to each other due to incompatibility.

In this situation I upgraded the backup gateway to 8.0.13
Now the client loses connection with backup and is forced to restart.
After client restart the tags have the values from before the failover. Except for the date in the UDT that has some garbage value from 1969.

Is there a way to solve this situation?
I don’t want to lose the data in the memory tags.

I think this is actually the same as this thread: [BUG-16628] DateTimes within UDT's are reset on Gateway Restart - not actually an issue with redundancy, just with the gateway restart. It’s (high) on our backlog to fix.

Thanks for the quick response.
But, I´m not convinced that this issues are related. When restarting the gw its only the memorytag with typte datetime that is reset. The other tags gets its last known value which is the value before the failover to backup is done in my example above. If I change the value of the tags when backup is active but before upgrading master. The master will have those values after upgrade and reboot. In my opinion things goes wrong when master cant take back control after the upgrade.
The manual says:
This allows the Backup to take over when the Master is down for an upgrade, and the Master can resume operations when it comes back online
The master does not resume operations, it gets active in parallell with the backup in my test and client is still connected to the backup. Both in the master gw and in the client diagnostics it says incompatibility problem. After the upgrade of the master the values cant be replicated back to the master for some reason.

Anyone have a clue how to not lose information during the upgrade?