Making the direction change at the end of the pattern section, where the block of tablets turning together to form the different-coloured stripe serves as orientation, though, works very well. It also has the nice side effect of keeping appearances neater - probably because the slightly increased wonkyness of the fabric is counteracted by the firmer structure of the several-turns-in-one-direction band.
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The two light triangles on the left are woven with the directional change at the start of the pattern, the ones to the right with the change at the end.
Or it was sloppier weaving on my part in the section before... or it was all the mistakes made. Hm. Whatever the reason - whether fewer mistakes or better weaving - it does look nicer now, and it is so, so much easier to work.
After figuring this out, I played around some more... and obviously I ran into some new, exciting (well, more or less exciting) problems. One of them was quickly solved, thanks to the input of the Most Patient Husband of Them All - I had accidentally done a second direction change after five picks instead of six. Odd numbers are, in this case, not a good idea, and five is right out. Aaaah. So you don't only have to tell left from right, count up to two (or multiples of two), and tell dark from light, you also have to tell odd from even.
That, though, is something I should be able to do. In fact, it's not hard at all - you just need to look at whether your shuttle is on one side or the other side of the band, and then remember that there is a "good side" and a "bad side" (which has no cookies, but horrible things in store for you) and only do direction change shenanigans when the shuttle is on the good side.
So next time I sit down at the band, there will be some Y shapes... and hopefully my current theory will work out.
Also up for getting solved? How to pour all these little rules and theories and things to know and keep track of into a format that will let others follow me when I talk about all this patterning craziness at the European Textile Forum...