Program received signal: “0”: If this is caused by memory leaks why do I not receive memory warnings?

After a few minutes of intense use my app quits with "Program received signal: “0”." As far as I've been able to determine this signal is caused by excessive memory usage. What puzzles me is that I often don't get any memory warnings at all prior to the app crashing. If I'm using too much memory shouldn't the OS emit a memory warning before booting me?

The only alternative that I can think of is that I'm requesting such a huge single block of m开发者_JAVA技巧emory that the OS just balks and boots me immediately, but that doesn't seem to be the case either: the crash often occurs in situations where there's no massive allocations of memory.

What am I not understanding about how memory warnings work or about signal 0?

P.S. - The app is an iPad only app compiled with the 4.3 SDK and targeting iOS 3.2 and above.