Hello, I have a related issue and I'm not positive if I'm encountering the Cache issue, propagating issue, or if what I'm seeing is the problem.
I've set the A record to the IP address for sub.domain.com directed by tumblr.
While setting up the CNAME for www.sub.domain.com to "domains.tumblr.com" and after submitting it is recorded as "domains.tumblr.com." with an extra dot at the end.
When I go to tumblr and click "test your domain" I try both www.sub.domain.com and sub.domain.com and receive a message saying that the CNAME is not pointing to "domains.tumblr.com"
After trying to change domains.tumblr.com. to domains.tumblr.com I get the following confirmation:
We have now edited the CNAME record for www.sub.domain.com with value domains.tumblr.com. to be the CNAME record for www.domain.com with value domains.tumblr.com.!
They're clearly adding a dot to the end, is this common or is this the issue?
Sorry to be overly detailed / repetitive, I was just hoping to get all of the info out right away.