[Question] DNS propagation delay handling

[lostmsu]

I wrote a DNS challenge provider for Cloudflare, and now experiencing an issue with the fact, that DNS changes do not always propagate instantly resulting in "DNS problem: NXDOMAIN" or "Incorrect TXT record" depending on existence of previous records.

I could implement polling but AFAIK my ISP DNS server returning the new TXT record does not guarantee that Let's Encrypt's one will.

Am I missing something? Should Lettuce be retrying?

Potentially related to #149