I’ve been inspecting for years, but saw something new today. I was checking GFCI’s in the kitchen. There were three normal receptacles in a chain connected to one GFCI. As I used my tester on each of the downstream receptacles, the GFCI that they were tied to tripped just like they should have. When I got to the actual GFCI and pressed the GFCI test button on my tester, nothing happened. I then pushed the built-in button on the receptacle and it tripped as it should have. I’m obviously going to write it up, but just wanted to know if anyone has seen this before, and what the cause might be.
As a matter of clarification since it has been mentioned by most people who have responded so far - all of the receptacles in question are properly grounded. I proved it with my standard cheap tester as well as with my Suretest.