Had to return my FZ200 for another one

Had a problem that developed with the EVF in that it had vertical lines that were very annoying and just not right. I took it back to the store and luckily they did have another one in the store so got a new replacement. Hopefully this won't occur again. Wondering if anyone else has noticed a problem like this or know why it would happen? They were very thin vertical lines all across the EVF and in not particular pattern.