Bad CRT causing retrace lines

The TV which I bought last started developing retrace lines after a month or so of use. I took it back to the lab for warranty (special deal) and had it examined by the real experts. They found that even with the filament supply disconnected and VG2 at 0V the screen would still light up. They could even see that the electrons weren't even coming from the cathode. That was with only the picture tube in a test rig. So in this case the obvious conclusion had to be that the tube was bad, and it was replaced (32" 16:9 SF, very $$). It had something to do with processing problems during manufacturing of the electron guns.
So even if this was a rare case, it *can* happen that retrace lines are due to a bad picture tube. It's more usual to suspect the VG2 (screen voltage) or a defect somewhere in the RGB video path.