Well, I just assumed it was symmetrical because I couldn't imagine it to be unrolled manually (I just quickly watched the visual representations of each side)... But now that you pointed out this I guess I'm going to check for differences, in all the filters. Do you remember on which side the typo was present?

And yeah, we still haven't really cracked the algorithm. I initially wanted to write the article as "understanding hqx", but I actually realized I still don't really get the rules.

Could you share the board post where you discuss your implementation?