I'm sorry to hear that some of your paper was fogged. At least you now know what's causing your safelight problem. I'd suggest that you also test any safelight you obtain (especially a free one) in the same way before trusting good paper to it. Some papers may not be safe under amber safelights; the instructions will usually give the manufacturer's safelight recommendations.
I haven't tried the Harman Positive paper, but it may be less sensitive to certain wavelengths of light than ordinary papers. Any fogging will show up as a reduction in contrast starting in the highlights. In fact, Harman says it's a very contrasty product and should be pre-flashed before some uses; this could be the reason you saw no fogging on it. That's a guess and I could be wrong.
Best of luck,