"too many timeout resolving $DOMAIN, disabling EDNS"?

[David Hagood <david hagood gmail com>]

Over the past couple of weeks I've been getting lots of messages like
this in my logs:

unexpected RCODE (SERVFAIL) resolving 'example.com/A/IN': 64.71.97.21#53
Aug  5 17:54:49 Deathwish named[1870]: too many timeouts resolving
'www.example.com/A' (in 'example.com'?): disabling EDNS

(where I have replaced the actual domain with "example.com")

This happens on MANY domains, not just a few, and on domains that I
would think would NOT be likely to have stupid problems (like Google and
Slashdot).

Has something changed in BIND that could cause this?