Well, that's bad news
On the other hand it's not very easy to spot by running a couple of control (static?) images for a couple of seconds (I assume that's how it works in QC), so I see how it can slip through.
I guess this means that:
a) LG has a bunch of faulty parts
b) they replaced the wrong part
c) they are all faulty, but only a few people see it because of different usage (lots of video content and games)
d) they are all faulty, but it shows only in particular configurations (like ours)
Try to go for an exchange (high risk BLB), or maybe you can get some technician on the phone to narrow down the thing.
I had high hopes