Incidentally, I had started a similiar problem in a Singapore pentax user forum, not sure can I cross link here.. but I will retype my contents here to share the information with Pentaxforum users.
12 Nov 2010
Title: Does your Kr/K5 work with 3rd party flash?
I had been using my 3rd party ebay OEM brand less PTTL flash on my Kx for almost 1 yr, and I have a "strange" encounter when i recently brought an Kr.
This OEM brand less PTTL flash works flawlessly on Kx and K7 at all settings (auto zoom head, sync aperture and iso. full PTTL function etc etc) and suffer no problem at all.
when the same flash is mounted on my Kr....at iso 100 200 it is still fine but any higher iso, almost every picture will be a white screen of death.....
I thought it is a flash socket problem with my Kr and went down for a chat at Emjay service center...Kevin slap on a AF360FGZ on my Kr....surprise surprise....it work fine....
Damn....so it means my brand less PTTL flash may not be so comparable to the new pentax models...
Any follow pentaxian here who own a 3rd party flash like Metz or Sigma PTTL flash, do they work on your Kr/K5??? I'm trying to gather some feedback, cos I have a event to shoot next week and I'm trying to gather some feedback, cos I have a event to shoot next week and I need a flash fast.....
In summary the response from Singapore user reported:
Flash made by sigma 530 Super, metz 48/58 and of course original pentax flash work fine with Kr/K5.
I myself had brought a Metz 50 and it work fine.
https://www.pentaxforums.com/forums/pentax-news-rumors/126529-d%F6rr-flashes-...ble-k-5-a.html