Hello,
First of all please excuse me if my english is unclear, I'm French...
I am experiencing the same kind of issue than the one described in this topic : http://forums.adobe.com/message/3943561#3943561, except I am using LR4.2, and a different camera. (Which is why I start a new topic, but feel free to merge it to the previous one if it is best for you).
I recently had a "strobist" photoshoot with my pentax K5. I thought I was in best conditions to obtain killer definition (2 off-camera strobes, iso 200, f4 with a samyang 85mm f1,4 which seems quite good to me and .pef raw file format). But it turns out that I got a weird cross hatch pattern on my pictures :
This is a 100% crop of an unprocessed raw from lightroom. The problem is clearly visible on both eyes...
Even weirder to me : different shots from the same session, taken with a tamron 17-50mm f2,8 (still @f4) do not show any pattern ! (Same camera, same setup, only differs by the lens and distance to the subject...)
I understood from the previous topic that it was a known issue that have been solved in LR3.6. (Which was a relief because I was searching all over the web for the origin of that issue...)
I tried the previous process (2010 & 2003), but the issue remain unchanged.
Do you have a solution for LR4 ?
I can send you the raw files (or any jpeg) if it can help you to analyze/solve the issue 
(By the way, I have been using lightroom for quite a time now, and I think you made a great job with this software !)