audiowizard,
Yes i did have the issue raise it's ugly head on my GT30 tv, it started just with greys on the set and then started to spread to the whites too with a strange tinge of green throughout these two colours.
Panasonic have indeed released an update although it's not a standard update and is more hardware related, it's carried out by an engineer via 3 seperate SD cards and takes about 10-15mins to complete. I had this update carried out to my tv and i have to admit it solved the issue entirely and hasn't messed up my set atall, all my settings remained intact (thank god) so no calibration was required after and i have not experienced any green blobs since with whites or greys or any other colour for that matter.
I can only go by my experience and that of others on this forum that had the update carried out and tell you that all of us that had the update carried out found that it solved the issue entirely and didn't affect the tv in any way afterwards so i would report the issue to Panasonic if it's under warranty and get the update carried out.
Panasonic are aware of the issue and i found that when i called them the customer service team knew exactly what the issue was and that an update needed to be carried out to solve it, i think in total it took a week or two for them to come out and install the update which wasn't bad. As far as i'm aware if any harm is caused to the tv via the update or if it fails to solve the issue then you are covered under your warranty, providing your tv is still under warranty of course, so you shouldn't be concerened about having the update applied to your set.
Hope that helps and keep me updated with what you decide to do 🙂