Image cropped when exporting to PNG

[kirko]

Hello,
I'm trying to export a 24x23px image (seen below magnified) into PNG file.
When I do that at Screen 72ppi, for some reason when it's all done it's cropped (as seen below in the example).

I tried exporting at High 300ppi (in which case nothing is cropped) and then resizing it in Corel Paint Shop, but in that case I have these "shadow effects" at 12 and 3 o'clock of the semicircle... the quality isn't great anyway.

Any idea why AI is cropping? I'm using CS4.

Thanks in advance.