Sorry if I am repeating someone else here, I havent read the whole thread.
The white lines are the VITC lines getting echo’d down the screen when you have a loop, ie both VT and FCP in EE. This is the same if you had a VT connected to itself or two VTs in a loop.
Putting the deck is PB mode does stop this but if the deck drops out of standby (or the tape is removed) it will revert to EE. Easiest way to stop this is to set your signal generator/SG (sony menu number 710) to Black Burst BB (option 14 IIRC) and when you are not playing back to the deck press and hold the SDI input button to engauge the SG.