The denial message reads, Header ”Pragma” without ”Cache-Control” prohibited for HTTP/1.1 requests.
(This is part of a series of new tests for spambots which claim to use the HTTP/1.1 protocol but actually do not do so properly.)
The trouble has been traced to a problem with those particular bots, and Syndic8 and PubSub have been notified.
Until they are able to fix their bots, you can add them to Bad Behavior’s whitelist.
Update: If you’re being blocked by Bad Behavior, don’t comment here. Read this.