Okay, found another klew to this issue... Apparently the pi is outputting video at a default 4K spec, and most of the TVs I'm using aren't accepting it, but one is....
Multiple lines of:
Then:
I would have played with the shell, but the machine is way up on a wall, and I had to transcribe the above from a photo of the screen. ^^;
Edit: And yes, I triple-checked the issue only pops up when the attached TV is turned off.