Aha!

It seemed like the experiment on the Mermaid Socks was working; I decided to stick with the pattern on 36 sts and do stockinette on the other 42. I did 16 rounds like that, then a short-row heel, and took another look at it. Hmm, the fishtail pattern stopped spiralling. Put it aside. Went to run some errands. Mulling it over, I realized that I could solve the problem by shifting where I start the patterning. It needs to start with the k2tog, so that the left-slanting ribs will blend into the stockinette, and end with the increase to offset the k2tog.

See? It has lost the slant:

So I have ripped back, and started the experiment again. I am 4 rows into it, and it looks like I may have it right this time. Oh, and I switched from a size 1 to a size 0 needle.

Thank you for the nice comments on these silly socks.

To answer Kristin (because I can't find a better way to do this), yes, I ordered 2 of the same color of the Kauni, in 2 different weight skeins. I haven't figured that part out -- whether each seller gets a random assortment of skein sizes, or whether I could have gotten 2 250g skeins instead of a 250 and a 240.

And now, since I have a paper to write (for Geometry!) that is due tomorrow at midnight, and family coming to visit tomorrow, I have to hide my knitting & do something that other people would define as productive. ;-)