OK, after banging on it for more than a few minutes, here's what I've noticed.
I ran xscreensaver-demo and made sure, that "Only One Screensaver" is the choice under Mode and that you should highlight Helix, then run
Code:
xscreensaver-command -lock
this works every time.
What I also noticed is that
Code:
xscreensaver-command -select 8 && xscreensaver-command -lock
works
once but doesn't work again after running it.
2nd attempt at terminal says
"xscreensaver-command: no screensaver is running on display :0.0"
even if I re-export DISPLAY=:0.0, it still bombs.
so, it appears to be one or the other as you have noticed. Can't select and lock.