Due to engineer performing their daily check and pulling this c/b to be able to check the strobe lights working on GND. A Std procedure since decades on the type among engineers worldwide.
I find this very strange, since we never pulled that breaker out during daily checks on our fleet. I worked with MD-80s and DC-9s for nearly ten years and never pulled the mentioned CB, ever. As I recall, on our fleet anyway, you could turn the strobes on turning a switch on the right hand side of the glareshield (it is possible I remember wrong, it's been a couple of years since I've been inside an MD).
Second thing is, you said they had reported thrust rating problems. Have I missed something? It is possible that I have missed such a piece after reading this thread through.