Addon domain no longer does masked redirect, but why?

Running - WHM 10.1.0 cPanel 10.2.0-R82
RedHat Enterprise 3 i686 - WHM X v3.1.0

Our newest cPanel server does not mask the redirection when doing an addon domain. Other cPanel servers we use does indeed mask the redirect. Any idea what may be going on here?

Also, everytime we do an addon domain we get this message:

Sorry, you are not allowed to park common domains.

Even though the domain is not a "common domain", i.e. it has been registered by the hosted customer and the DNS is correct, i.e. it is directing traffic to the proper server, etc.

By the way, we get this message no matter how the "tweak settings" options for this in WHM are set.

My guess is that the addon domain is hitting an error before being established fully/correctly.

Can anyone shed any light on what may be happening?

 

As it turns out, the other redirect the hosted customer had established was interferrring.