2.6.x "cxnsleep transfer permission denied"?

[Nix]

On 24 Jan 2018, Nix spake thusly:

> 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.

Speculation: is this because I'm suddenly connecting to/from all my
peers via their IPv6 addresses, but they only know to grant me
permission to read/post over IPv4? If so, it's *really annoying* that I
can't turn IPv6 off temporarily until my peers have been informed of my
IPv6 address :(