[Brightcolours]

The glass is the same. The coatings are the same, despite pentax marketing blurb. A rebadged Pentax.

The Tamron is better (renders quite a bit nicer, without the CA issue)

You're just trolling.
First, you don't have a way of knowing if lens elements or coatings are the same.
Second, the lens is not a rebadge but a customization of the Tamron. There are physical differences, besides the cosmetic outer ones, the mount and electronics/firmware.
Third, you're lying that the Tamron is better.

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Nuh, I am stating simple facts.

First, we do know the elements are the same. Pentax only decided to point out a 2nd kind of glass more than Tamron did. You can't just exchange one element of the same shape, in the same configuration, with glass that had different dispersion characteristics, and expect good results. 
We also know that the coatings are the same. Just because Pentax decides to call their coatings "HD" means nothing, except maybe for Pentax fanboys. Canon, Nikon, Tamron, Sigma, Sony, Zeiss, Pentax update their coatings as the technology in the sector advances, and this Tamron lens uses... good Tamron coatings. The "SP" Pentax nonsense reads as follows: 

"This lens features SP (Super Protect) Coating on its front surface. Applied by means of a PENTAX-exclusive fluorine deposition process, this coating is highly repellent to water, grease and dirt, making it easy to wipe off stains such as fingerprints. This frees the photographer from worries in outdoor photography.OTE:About KAF4 lens mount"

Exclusive... Right. Except that Nikon, Canon and others (including Tamron) also use such a fluorine coating for exactly the same purpose. 

Lets read what Tamron writes about this Tamron lens:

"Fluorine Coating for protection and safe cleaning

The front surface of the lens element is coated with a protective fluorine compound that is water- and oil-repellant. The lens surface is easier to wipe clean and is less vulnerable to the damaging effects of dirt, dust, moisture and fingerprints."

Oh, right.

Second, the lens is rebadged Tamron, built by Tamron just like the Canon and Nikon version are built by Tamron. There are physical differences, besides the cosmetic outer ones: the mount and electronics/firmware, between all 3 versions. Only the Canon and Nikon version, with VC, focus fast due to Canon and Nikon bodies, and the Pentax version will focus slower and more hesitant, so they felt the need to put the now VC-redundant button to use as a focus limiter.

Third, you are silly calling that a lie. The Tamron is a better lens. It renders.. better. It has... way less CA. It does not... shrink to 135mm at MFD like the Pentax does. The Tamron is objectively better.