This "problem" has been going on for years concerning Pentax digital bodies.
Some lenses I own, have come pretty close to touching the upper part, just above the lens mount, on the front of the camera.
To be honest, with every new Pentax body, I look for this space, and it's very close on a number of lenses.
I hate to say it, but this is a Pentax oversight for not anticipating more clearance just off the lens mount.
Some lenses get immediately "fat" just off the lens mount, and Pentax should have given just a bit more clearance.
Sigma seems to have other problems, but this lens-scratch thing, is definitely a Pentax oversight.
I have a Bigma, and I am happy to know I need to be careful or not mount it if I can't live with a little scratch.
Additionally, the pressure to make that scratch, is probably enough to lift the lens mount so the contacts short out, or the camera freezes.
Thus, we now have the mechanical reason for Sigma lenses to be freaking out when they are attached to a K1.
Once you get the scratch/groove, I'll bet Sigma lenses work just fine.
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See my comments below as I learn more about how Sigma lenses have a wider lens mount****
Last edited by LaurenOE; 05-11-2016 at 10:40 AM.