Question about stacked TC's... Only 1 stop lost?

I just received my second Tamron TC (1.4x) Pro today. I stacked them, expecting to be at f/8 for shooting, since I would loose two stops of light. To my surprise, it was limited to f/5.6... So I thought ok, the second must not be reporting. So I took test shot at f/5.6 and exposure looked fine. Put it up to f/8 and it looked identical (although greater field of depth). Also, AF is working fine, although a little slower to lock on. But it seems to be accurate once it does lock.

Is there something I am missing here with this? Why is not the f/5.6 dark or show any signs of flaw? I was expecting to have to shoot at f/8 but it looks like I may not need to...

Appreciate the help!!

IIRC only the TC connected to the camera is "counted" when the minimum aperture is figured (crazy, but pretty sure its true).

EDIT: Since metering is TTL (through the lens), it doesn't matter what aperture the body "thinks" its at, the metering system compensates for reality.

Ohhh ok! I just tested it and you are correct. With 1TC at f/5.6 I get shutter speeds of 1/10, and with 2 TC at f/5.6 I get 1/4.

Appreciate it, thank you!