Further to that issue, I've noticed the lens model doesn't get picked up by the site's exif display even when it is present in the actual photo's exif. (Having solved why it wasn't always getting picked up in that.) This seems to be part of the site's software that needs sorting out. FWIW my own Piwigo gallery software manages to capture the exif for this OK when present whilst the gallery here consistently fails to do so. It just shows it as undefined; but it definitely is (defined!)

I suspected Chris wasn't after a FA28-105 at all so probably wasn't relevant. Though just making sure. You're quite right though.

What you're asking for is something quite subjective. But there is a site where older Pentax lenses are compared which would put a numerical value on those comparisons rather than opinion.
See: http://www.takinami.com/yoshihiko/photo/lens_test/pentax_35.html
You'll see that the 50mm macro lens peaks much higher than the 35mm f2. I suspect the 50mm f/2,8 macro could well be the sharpest Pentax lens.
For some reason they haven't tested the FA31Ltd but I've no complaints about mine - however that's subjective!
Have you tried the DA 35mm f2.4? Despite theoretically being a crop sensor lens it does cover the full frame circle and is said to be optically based on the FA35. For what they cost (not a lot) it might be worth a try. Then with the money saved put it towards an even wider prime. The DA35 is optimised for digital sensors unlike the FA35 which was designed for film use.
Otherwise, hang on for a bit as there is a wide angle prime for the K-1 on the Pentax FF road map scheduled for release this year. https://www.ephotozine.com/article/pentax-lens-road-maps-revealed--29957

This is an ancient thread about asking Pentax themselves while your query is about a problem with this site.
I've checked one of my photos in the gallery such as: https://www.pentaxuser.com/photo/comp-693/grosmont-to-york-97160 which was taken on a K-S1 and you'll see the exif shows fine.
As the actual exif on your K-S2 images looks fine too it seems its getting misread somehow by the site's software that shows it. (I can see what you mean and see it as you describe on your gallery images.)
Suggest you use the 'report problem' button at the bottom of every page from one of your affected gallery images so the site team can investigate it for you. My presumption is that your image processing software has changed something when it re-saves the exif that confuses the site. But how or why I've no idea!

Just to clarify, do you mean the FA28-105 (the old film one) or the new DFA28-105? I've got one of each but alas, they're both stopping here! I presume you're after the new one.
I mention it in case you didn't realise there are two varieties of it and you obtain the wrong one by mistake. The old one's OK, but not as good as the new DFA.

The amazing thing about that one is how small it is and how little it weighs. Then compare it to the 15-30 brick! The brick maybe optically better but there's nothing wrong with titch. One's more likely to have titch in the gadget bag than the brick because of the weight. 203 grams compared to 1040 grams

The DFA 28-105 you mention is a good all round general purpose lens for the K-1, nothing really wrong with it at all and no dearer than many third party lenses. The FA24-90 makes a good runner up to it at less cost if you can track one down.
The other DFA lenses that cover the basic range are the15-30, 24-70, 70-200. They too are fine lenses but not cheap. If new ones are too dear just wait for a second hand one to turn up?
For less costly options, rather than ask about specific lenses which others haven't got for use with the K-1, why not ask what others actually use?
Alternatives to the 15-30 are the FAJ18-35 (an OK lens for what it costs and does) at a fraction of the price and/or a Samyang 14mm f/2,8 prime (an excellent lens) or wider still, the Samyang 12mm fish-eye (also a sharp lens.) The Sigma 17-35 you mention also covers this range but I've not seen one to try and reviews suggest it doesn't impress (Tamron do a 17-35 too.)
There's plenty of alternatives to the 24-70 such as the Pentax's mentioned above, offerings from Sigma and others. I think you'd be better off with one of the Pentax's rather than the Tamron 28-75 you mentioned (but I haven't seen the Tamron let alone try one.) I suppose it depends how important f/2.8 is to you. The DFA 28-105 would be a good lens to start off with if cost is an issue.
The Tamron 70-200 f/2.8 does make a good alternative to the new Pentax one but it isn't weather sealed. There's also a Sigma that covers this range but now discontinued and hard to find.
That seems to cover the range you queried. The lenses I've suggested I have tried/own unless I've said otherwise but I can't really comment on a lens I've never seen and lack of comments here suggests others haven't either! Therefore for reviews you'll need to look at the reviews on a number of sites with the help of Google, possibly even having to read about the lens tested on a non Pentax camera (are there other camera brands!??)

Yes, me too. They're not cheap though, are they? Any camera over £1500 isn't exactly a consumer model (so my insurance company tells me!) I just consider a professional to be someone who makes a living from photography, not what camera they use, and some of them wouldn't spend that much on kit.
By premium I mean expensive and if someone's new to the system the lenses they'll find at the dealers will be the DFA's, normally not the third party offerings.
(Same as when a Canikon user buys his camera and gets the Canikon lenses to go with it.)

So how many systems are you running?
Pentax Q; Pentax K; OM-D. You must have a huge gadget bag for that lot before you load any lenses!

Has it been knocked / dropped?