Deadwood's recursive resolution is not bug-for-bug identical to BIND's
recursive resolution; I have, ever since the beginning of 2015, have
not had time to fix these issues. This in mind, if using root_servers,
a small number of misconfigured domains which resolve in BIND anyway do
not resolve in Deadwood. These are the known issues:

*   MaraDNS does not resolve RFC-violating CNAME records
    combined with other records the way BIND does. Discussion:
    http://samiam.org/blog/2015-02-11.html

*   MaraDNS does not handle out-of-bailiwick glue records
    for CNAME records the way BIND does. Discussion:
    http://samiam.org/blog/2016-07-21.html#MaraDNS_Not_chasing_moving_goalposts

*   MaraDNS does not handle out-of-bailiwick glue records for NS referrals
    the way BIND does.

The first issue is caused because CNAME records with other records
downright violate the RFCs, so there's no standardized behavior for
handling them. The second and third issue are caused because older
versions of BIND handled them differently than newer versions of BIND;
MaraDNS' recursive algorithm was designed in 2001 to emulated BIND's
older behavior, and the 2010 recursive rewrite used the same algorithm.

If I were to win the lottery, allowing me to retire early, I would have
time to fix these issues -- but right now I do not. 

In other words, use upstream_servers instead of root_servers unless 
you're willing to fork MaraDNS/Deadwood and Use The Source Luke (UTSL)
to fix the bugs.