isearch behavior with <delete>

[Carl Offner]

I'm currently using emacs 21.1.  In some previous version of emacs, if
I were to search (using isearch) for a string and then realized that I
typed one or more wrong characters, I could delete successive
characters from the end of the search string by using the delete key.

In the current version, however, the first delete ends the search and
successive deletes wipe out characters in the file I'm editing.

Is there any way to customize the behavior of isearch to restore the
older behavior?

        --Carl Offner