Comment # 1 on bug 1199259 from Jonathan Kang

(In reply to Rainer Sabelka from comment #0)
> User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:99.0) Gecko/20100101
> Firefox/99.0
> Build Identifier: 
> 
> I use NetworkManager to connect to an OpenVPN private network, which has
> it's own internal DNS-Servers.
> DNS lookups are cached by nscd.
> Ater I disconnect the VPN, DNS names which were resolved via the VPN DNS
> servers still have those VPN address.

Are those DNS servers still available in /etc/resolv.conf?