Had a second look at my prints today in good daylight, and I'm an idiot: those blue shadows are just because I forgot to substract about 5Y. My whites were looking all dandy, but of course a faint blue cast on white is not always obvious to the untrained eye. When I noticed the neutral shadows of another shot, I realized my mistake.
But it's true that this film does not like indoor or overcast days. Portra is a much, much better film for these situations. Ektar 100 is my new vacation film: it gives us the nice bright colours, and the greens of summer. Makes you think all the world's a sunny place.