Problems with K110D and battery grip.

I recently bought a battery grip for my K110D. I use the camera for sports and wildlife, and have the autofocus set to continuous most of the time. This sucks the life from even the best re-chargeables in no time so the grip looked like a blessing. It arrived quickly and I was impressed by how well it fit the camera and how good the brief instructions were. The camera felt ....zippier like a fresh set of batteries had been fitted hot from the charger.

Ok so the grip came from eBay (alright, alright I can hear you all groaning and tutting) but I researched it carefully before shelling out £50 and I couldn't find a bad word about it.

Now the problem, about 1 shot in 10 the mirror fails to return properly. The viewfinder is out of focus and the camera flicks the mirror up and down until the problem is resolved. While this is going on any button on the camera will make it flick the mirror. It might happen five times in a row, it might not happen for 20 shots. It doesn't happen when I remove the lens leading me to think that it is tied into the aperture mechanics as they appear to be linked. The problem is much worse when I use my Tamron adaptall and happens with all the lenses except my mirror which has no aperture settings.

Now for the freaky bit, If I put the re-chargeables back in it doesn't do it.

I contacted Pentax's service department and got the standard "bring it in, It'll take a month and cost about what a new body will to have a look at it."

Gutted, anyone out there have a similar issue, any Pentax engineer tell me why a slightly increased voltage, (6.2v as opposed to 5.65v for the re-chargeables) would stop the aperture/mirror from re setting?