Having built LEDE from source (a69e19d) I realized that nslookup (which is built into BusyBox) is behaving weirdly. Invoking it from command line via SSH I get an error message, although the name resolution is still working:
root@rtr1:~# nslookup google.com
nslookup: can't resolve '(null)': Name does not resolve
Query the nameserver for the IP address of the given HOST
optionally using a specified DNS server
The [SERVER] parameter can be used to query a specific name server. This does NOT work. Regardless of what I put there, it is always the default resolver that is being queried. I am not able to query a specific nameserver, which in my case makes a difference (split horizon DNS).
For instance this query shouldn't return anything since my nameserver (ns1.babioch.de) is not configured to answer recursively: