I have had the mirror flutter problem. It happened only once, shortly after I first received my K-3 from B&H on Nov. 13, 2013. My camera's serial number is 4833996. The mirror started flopping machine-gun style. Panicking, I turned the camera off - it continued to flutter. I do not know what the settings were on the camera, but I usually shoot in aperture priority, single shots only. I began to attempt removing the battery, but before I could do that, it ceased fluttering. The firmware at the time was v. 1.00. I have since upgraded the firmware with versions 1.01, 1.02, and 1.03, but have had no further recurrences of the flutter. At the time of the incident, I was not using the battery grip, I was using only a 32 GB SanDisk Extreme memory card in slot one. Slot 2 was unused. Routinely, when a battery shows any depletion at all, I rotate it with a fully charged one, so I believe the Pentax battery was fully charged or almost so. My lens was the Pentax 18-135 WR. Daytime temperatures at that time in Phoenix were probably around 65-70 degrees F. I'm sure I had less than 500 shots logged on the camera at the time. I'm pretty sure I was on autofocus.
Looking through the viewfinder after the flutter, it was impossible to see anything, so it appears the mirror was left in the "up" position. Turning the camera on again, I checked for any photos taken, but none were, and the camera worked normally. I have been using it off and on (maybe 3 or 4 pictures a week on average), but have not experienced the "flutter" since. I would be very interested to know if Pentax is aware of this annoying problem, and if they are going to do anything about it. If a firmware fix will take care of it, I hope it comes out soon.
John
Last edited by PALADIN85020; 03-13-2014 at 12:06 PM.