I have a file which is 1020px X 200px Artboard/Document dimensions and the drawings coves the whole artboard as follows.

When I "Export" the file as "png" (File>Export) it's dimensions change to 4250px X 458px as follows.

However when I use "Save for Web & Devices" (File>Save for Web & Devices" and save as "png" it's dimensions remain the same i.e., 1020px X 100px as follows.

Any idea why this is happening? Files are saved with similiar options viz. png-24 format, clip to artboard, save as background, interlaced, rgb color profile.
