On the comma trick:
I created new brain with home thought foo, then children 1, 2, and 3, then child "1, 2, 3" of 1, then linked grandchild to each of 2 and 3 as parents, and sure enough, got the predicted behavior when and only when 1, 2, or 3 is the selected thought.
1. Um, why would one want this behavior?
I then created new children of foo as red, green, and blue, then child "red, green, blue" of red, then linked new grandchild to each of green and blue as parents. Once again, I got the predicted behavior.
However, when I now select 1, 2, or 3, I no longer get the predicted behavior for "1, 2, 3". It appears that only the latest grandchild created in this way works, which leads me to...
2. Is this just a bug at this point? Not only do I not understand why one would want the behavior, but it also doesn't work most of the time.