Uploaded .png grows

That happens sometimes for images with large dimensions - i.e. pixel sizes larger than 800 wide or long. We've set the forum to only display up to 800 pixels for normal inline display, so, when an image larger than that is uploaded, it needs to be processed to allow resizing. The one you were working with was a full 1024 pixels wide, so it was processed on the server to allow for resizing. The processing can cause a growth in filesize, though sometimes it reduces filesize. PNGs tend to grow. JPGs tend to shrink.