Another <Backspace> Question

I had posted a question asking if there was a way to disable the backspace key on a web form. Because I had users complaining that when they hit the backspace key on a drop down or option, or check box it took them to the previous page.

I found a javascript that altered the ASCII value of the backspace key that eliminated the issue.

However it worked too good. What I would really like is for the backspace to be disabled on the drop down, option, and check box controls and re enabled on text controls. One funny thing I noticed is that the backspace does continue to work on single line text boxes but not multiline. Code: