Indeed. This is why I was wondering if the OP was using a completely opaque material to cover with while doing the test strip.
That's the only reason I can think of why the exposure from the test strip wouldn't translate.
I guess to find out whether it's opaque or not could be found out by simply covering the entire print area with the material and shine the enlarger light on it. Never uncover the paper, and then develop it to see if any density was accumulated or not.
The same test could be done to see if any stray ambient light hit the paper surface during the making of the test strip.
Just some thoughts.