26.1.1: Unbound: Option "query forwarding"->"Unexpected error, check log for."

[rolsch]

After updating to 26.1.1 today,
I switched from ISC DHCP to DNSMASQ (where I mainly use static IP‑MAC mappings).
After that, I migrated the firewall rules to Rules (new).
So far, so good.

Now I've noticed a strange behavior:
As soon as I enable the option "Use system nameservers" under Services → Unbound → Query Forwarding,
a red warning popup appears saying "Unexpected error, check log for details" along with the message "There are no system nameservers configured. Please do so in System: Settings: General."

However, I do have four DNS servers configured there, and two of them have a WAN interface assigned.

If I disable this option, Unbound uses the ISP DNS servers and
I can switch back and forth between the nav-points:

Services → Unbound DNS → Query Forwarding 
and

Services → Unbound DNS → DNS over TLS

without any error.

If I enable the option again,
the error message appears, but Unbound still uses the DNS server list.
It also seems that this option becomes active immediately after checking the box,
even without explicitly saving — restarting Unbound is enough.

I believe that in version 25.x.x I had this option enabled without any error.

[rolsch]

- also diese Meldung bekomme ich nicht weg...

[rolsch]

I have deleted, saved the dns entrys in the System: Settings: General.
Restarted the system and enter again the dns-server in System: Settings: General.

But the DANGER message pop up in the two sections:

Services → Unbound DNS → Query Forwarding
Services → Unbound DNS → DNS over TLS

So what the heck is wrong...?????