Turning off tube preamp first sends solid state amp into protection?


I have been experimenting with using a vintage Luxman CL40 valve preamp as a separate preamp stage for my L-509X integrated. Because I leave the solid state amp on 24/7, I accidentally turned off the preamp while the 509X was still in Separate mode. The integrated immediately went into protection mode with the power light blinking. I powered it down into standby mode, then brought it back up and it remained in protection mode. It wasn't until I unplugged the 509X and plugged it back in that everything was cool. 

Did I do any potential damage here? What it it happens again? It's pretty easy to accidentally turn off the preamp when I'm leaving the 509X on all the time.
128x128jsqt
Don’t be lazy.

The rule is quite simple: preamp on first, amplifier on last. Reverse for off.

Its easy. Really. It is.
Guy walks in to his doctor's office and says "Doctor it hurts when I do this." Doctor says "don't do that."  Henny Youngman
I follow the jeenam and imhififan order: 

ALWAYS power the amp on last!
ALWAYS power the amp off first!

It works for me.