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.
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Does it matter though, if all components in the chain have mute functions ? I’ve always been curious about this. Out of habit I always follow the above mentioned sequencing, and also leave everything muted during the process, but wonder if it really matters, as long as I un-mute (or mute) in correct sequence. Any thoughts ?

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.

L.O.F.O  - Last On First Off