Originally posted by BillO FWIW, I can personally say that the *istD, K10D and K7 (all flagships during their debut) I have owned and all with 100K+ shutter releases have never had a problem like this. Or a lock-up.
That may be because Pentax dSLRs prior to the K-5 had no history of a pattern of mirror or shutter issues.
As I remember, the classic mirror flop (a.k.a. double slap...mirror flips twice...also various other mirror control issues) occurred over a limited range of K-5 serial numbers first reported in 2011. The cause was traceable to a defective hardware subsystem (bad batch) that was replaced under warranty. Similar symptoms were noted on the K-r with additional problems described as random mirror activity not associated with shutter use also being reported. With a few users the mirror would flap when any button was pushed. Some of the problems on the K-r were traced to power issues (bad batteries/holders). A few users only had the problem when certain lenses were mounted (?!). I don't know if the issues were ever fully characterized or resolved on the K-r, but the remedy involved replacement of the camera's main board and/or mirror box.
It should be noted that the K-5 technology was based on the earlier K-7 model and that the K-r was based on the earlier K-m. Both the K-5 and the K-r were Pentax products designed and made under Hoya ownership while the K-3 is a Pentax-branded Ricoh product. Ricoh purchased Pentax in late 2011 so the earlier K-5 and K-r issues were not the result of Ricoh design or manufacturing process.
To the best of my knowledge, the following models had no reported pattern of mirror issues: K-5II, K-5IIs, K-30, and all models prior to the K-5.
As noted on this thread and other places in PF and on the Web, a number of K-3 users have experienced what has been described as a "runnaway", "crazy", "machine gun", "uncontrolled", etc. mirror behavior. The symptoms are different than the K-5 "flop", but similar to what some K-r users described a few years ago. The K-3 issue is being addressed through adjustment of settings in firmware at the service facility.
To complete the rogue's gallery, some K-50 users have had a problem that has been labeled "mirror flap", but is basically a full system freeze with the mirror in the up position. The issue is being addressed by Ricoh by replacement of the mirror box and/or other drive components. No, it is not another mirror flop/flap issue.
Summary? Prior to the K-5, mirror control issues were essentially absent from the Pentax line. Three models in the last three years (K-5, K-r, and K-3) have had reported mirror control issues. The three models represent three distinct model lines with three different sets of symptoms and remedies. While it is unlikely that the three share a common cause, it does point up to (IMHO) a distinct blind spot in Pentax (initially) and Ricoh's (now) QA efforts, though it is difficult to say how they should test for something that is difficult to demonstrate even in known bad bodies.
Steve
P.S. The descriptions above are not exhaustive. The data are widely scattered.