I'm adding my two cents here.
Last year, I had 3 50VT30, all with green blobs from the start. I kept one for over 500 hours to see if issue would solve itself but it never happened. So Panasonic maintenance service accepted to refund me.
I then bought a 50VT50 that had a green blob which I spotted immediately, on the first turn on. I had it swapped for a 50ST50 that was perfect save for a slight vertical banding on right edge.
Kept it for 10 months until, after the 1000 hours mark, the vertical banding became more visible and widespread (5 vertical bands). I also had a large red blob at the center (visible on white and grey backgrounds) and brighter left and right edges (visible on black screens).
Screen was sent for repair to Panasonic 3 weeks ago. Last week, I was told that Panasonic technical services refused to repair or refund, arguing that this non-uniformity was normal and would solved itself over time. They even said that the screen hadn't broken itself yet (even though I was over 1000 hours !!!).
I therefore personally called Panasonic 2 days ago and fought over the phone for one hour, explaining that I knew what I was talking about, that this uniformity issues had appeared over time, ...
In the end, after a long-fought battle, Panasonic accepted to refund me. I am waiting to hear from my reseller as the refund passes though them first (that's how it works here, in France at least).
I will then have the choice : 50ST60 (but I'm fed up with Panasonic as a whole) or try Samsung new F8000 LED TV as they supposedly solved the clouding problem with their new microdimming technology.