Sound card problems?

The computer has a Creative Soundblaster AudioPCI 64D sound card. There is a speaker extension cord plugged into the sound card, leading up to the top of the desk to make it easy to switch between speakers and headphones. This setup works fine on another computer. However, on this computer, if the extension cord is plugged in with the speaker attached first, then only the speakers work. If you try to plug headphones into the extension cord, they won’t work. However, if the headphones are attached first when the extension cord is plugged in, they work fine. Then, the speaker won’t work. Why is this?