PNG smilies uploading in JPG - why?

Hello,
I am experiencing a problem at L4W2 Gamers, my forum.
I
For some weird reason, when I upload a Smilie that is a PNG, that Smilie seems to end up with a black background where the transparent part is.

The same glitch occurs with GIFs, they won't animate at all.

I am uploading from a PC now, by the way.
Before these PC uploads, I uploaded about 15 JPG smilies, may this be the reason why this glitch occurs? Because the system is used to JPEG format for latest Smilies, it can't work with anything else?

Try clearing your browser's cache.

Hello Luigi442wii,

What is the size of the file you're uploading ? If it is above 1mb, or large in dimensions it will be converted to JPEG.

About 500-600 Pixels.
By the way, I want to upload a smilie for :3 but it appears as :3: