Upgraded PHP to 5.2, and phpicalendar promptly broke. Silently. That is, I was getting the White Page Of Death, but no error messages, even on E_ALL.
The short form of the story is that by increasing memory_limit (it was set to 11M) the problem was solved. When PHP encounters the memory_limit, it simply bails silently, without logging any kind of error message. That’s unfortunate.
So it appears that under 5.0, phpicalendar was able to run without problem in 11M, but with 5.2, suddenly it requires more than that. Exactly how much more than that, I don’t know, and didn’t experiment a whole lot. Perhaps that’s a task for another day.