http://keybase5btp2qikoau6u326pvotn47gb55mo6fjxxyxdoywiinomr5id.onion/blog/chat-apps-softer-than-tofu
We can also attribute this bug to added complexity required to support both
sigchain V1 and sigchain V2 simultaneously. Modern clients write sigchain V2
links, but all clients need to support legacy V1 links indefinitely. Recall
that clients sign links with their private per-device keys.