First of all, thank you all for tuning in. I have tried the suggestions from both @RoseHawk and @Snarlygribbly, though I am sad to say neither made any difference. I ran more tests with various settings, using different scenes I made over the last years and some new test ones. The baseline for me seems to be that Superfly simply ignores certain settings for lights. When rendering the same scenes with Firefly, shadows behave as they did before in Poser 11.3.

I will follow the advice by @hborre and submit a ticket, because I have the sneaking suspicion this may actually be a bug and not, as I first suspected, user error. ^_^"

Again, thanks to all of you. :-)

Run, wolf warrior, to realms eternal....