securityheaders follows redirect that doesn't exist

[weinzierl]

Submitting weinzierlweb.com to securityheaders.com actually scans unstable.weinzierlweb.com

If I'm not completely confused there is no such redirect and has not been in the recent past. There is no HTTP redirect, both domains return 200, serve different pages and show different content in the browser. Their DNS records point to different IPs as follows:

• weinzierlweb.com
  A 46.101.253.80
  AAAA

• unstable.weinzierlweb.com
  no A record
  AAAA 2a03:b0c0:3:d0:0:0:70:d001

Note that the second domain is IPv6 only.

Other tools properly report the correct site:

These are not cached reports as you can see from the dates. They were made roughly at the same time I did the securityheaders.com report.

This is most probably a strange and minor corner case but I thought I report it.
I'm curious what is going on here. Thanks for making securityheaders.com freely available!