[Brian]

Aha; it looks like nested contexts are responsible for what I was seeing. Within each branch/level of the tree, the contexts are alphabetized, but an action in a parent context will appear above any actions in the child contexts.

So, "Errands" appears at the top of my list, even though it isn't at the top of the sidebar. Similarly, it's followed by "Errands : Apple Store", even though that context is below "Book Store" in the sidebar.

Feature request for the option to use sidebar order written up, in any case. :-)