PTP mode does not support Bulb mode. You need to switch to MSC mode. Honestly, unless you need live video, you may just want to forget about PTP mode (though I welcome testing).
In either mode, the Native driver (I cannot speak for gPhoto/legacy) is highly untested, unfortunately. The most feedback I ever received on it was from people using older camera models that ultimately just wouldn't work. The K-70, on the other hand, should work well, ideally, so I really appreciate feedback like yours. Could you let me know which OS you're using, as well as the specific hardware you're running on?
The Native driver hasn't changed in a few months. I'm not sure how far behind Astroberry is, but last time I tried it I think it was fairly up-to-date, so I doubt that an upgrade affected anything.
I need to investigate the SD card issue--I thought that worked, but it's not part of my normal process flow. I usually just save to the client. I'm on an extended road trip right now, so it may be a week or two before I have my equipment available to test.