Can't change dns record to internal ip if current ip is public and has proxied = true

[JorritSalverda]

When changing a dns record from public and proxied to internal it fails with

{
  "time":"2019-04-24T07:42:38Z",
  "severity":"error",
  "app":"estafette-cloudflare-dns",
  "version":"1.1.2",
  "error":"Updating cloudflare dns record failed | [map[code:1004 message:DNS Validation Error error_chain:[map[code:9041 message:This DNS record cannot be proxied - click the cloud icon to turn it gray to proceed]]]] | []",
  "message":"Processing ingress *** failed"
}