I believe the answer is found at this website:
http://www.beyondlogic.org/spp/parallel.htm"Note: Some control ports are not open collector, but have totem pole outputs. This is also the case with EPP and ECP Ports. Normally when you place a Parallel Port in ECP or EPP mode, the control port becomes totem pole outputs only.."
I think the behavior I'm seeing is the "open collector" output unique to a few pins, including pin 16. The PC is able to pull that pin low, and there's a pull-up resistor to bring it high. I even put my own pull-up on there just in case and that didn't work.
This tells me that the G540 loads that pin down too much, and the only fix is EPP mode or to put a buffer. We'll see what they say. If the answer is "EPP" then I will be surprised. I see so many people hitting this issue and are tossing perfectly good parallel port cards simply because of a missing buffer between pin 16 and the logic in the G540.
This also explains why when I "broke out" pin 16 to a breadboard and put a logic gate (basically made my own buffer) and THEN fed the G540 it worked. If this is indeed the problem, I hope GeckoDrive does the right thing and puts a buffer in rev3 of their product.
Hopefully there's a better fix forthcoming from the Gecko guys, but I'm going to make a small buffer circuit in the gender changer before I toss my parallel port card.
-Tj