I set up a reminder to myself at the end of the month. Guess what happened on Feb 29? Right, calendar switched to March silently, since there was no Feb 30. Which is a reminder that programmer’s logic is usually something completely different from people’s logic.
P.S. there’s a special setting in Calendar.app to get exactly what I want, but it seems to be buried deep down and, from the looks of it, Apple doesn’t really work on it all that often (see spacing between controls, calendar grid alignment, black border instead of light one, the fact that Ok/Cancel button were cut off by the edge of the screen).