http://www.renderosity.com/mod/forumpro/showthread.php?message_id=4017040&ebot_calc_page#message_4017040

I searched only for the word "small", posts by me. First match was it.

Note: The solution has nothing to do with adding a figure. The figure works, but does so because it is large, not because it is a figure. Anything large (or more precisely anything that enlarges the scene bounding box to be over a foot) will fix it.

Note also that the symptom may be that the shadow is a rectangle, or it may be that the object is black. The latter is when the mistaken rectangular shadow also happens to perform the mysterious self-shadowing that Firefly is so fond of doing in an infinite number of ways.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)