iphone ios version 3.2 and earlier -- button background image rendering

I am developing code for ios 4.0.1 that I am now testing with earlier versions. My problems begins with ios verison 3.2 and earlier.

I notice m开发者_Python百科y buttons with background images are being rendered at full size. The images are 512x512 but the button size is 41x41. Maybe what I did is just a bad practice.

My real question is where can I find the documentation for the ios version changes that would identify this change in behavior?