2.6.x "cxnsleep transfer permission denied"?

[Nix]

So I just upgraded to 2.6.x latest (from 2.5 as of mid-2015), and now
every single one of my feeds is saying this:

Jan 24 21:49:45 loom warning: kzdoos.xs4all.nl:0 cxnsleep transfer permission denied
Jan 24 21:49:45 loom notice: kzdoos.xs4all.nl checkpoint seconds 0 offered 1 accepted 0 refused 0 rejected 0 missing 0 accsize 0 rejsize 0 spooled 0 on_close 0 unspooled 1 deferred 0/0.0 requeued 1 queue 0.0/200:100,0,0,0,0,0
Jan 24 21:49:45 loom notice: kzdoos.xs4all.nl final seconds 0 offered 1 accepted 0 refused 0 rejected 0 missing 0 accsize 0 rejsize 0 spooled 0 on_close 0 unspooled 1 deferred 0/0.0 requeued 1 queue 0.0/200:100,0,0,0,0,0
Jan 24 21:50:15 loom notice: kzdoos.xs4all.nl:0 connected
Jan 24 21:50:15 loom notice: kzdoos.xs4all.nl remote MODE STREAM failed
Jan 24 21:50:15 loom notice: kzdoos.xs4all.nl checkpoint seconds 30 spooled 1 on_close 1 sleeping 0
Jan 24 21:50:15 loom notice: kzdoos.xs4all.nl final seconds 30 spooled 1 on_close 1 sleeping 0

It is... less than clear what "cxnsleep transfer permission denied"
means, or even whether it comes from my end or the other end: from the
source, it appears to be in response to a "480 Transfer permission
denied", but who is emitting this response and why is less than clear.
Incoming news seems to be flowing, and though I'm not sure yet about
outgoing innfeed's statistics suggest that things are fine.

(It is also less than clear why this has suddenly started happening in
2.6 when I left the config files utterly unchanged from 2.5 specifically
to stop anything like this from happening. Maybe it's just a new
message, and the condition is old?)