DuaneB:
I assume its a memory leak as my understanding is that delete does not free memory in Arduino and the current implementation of detach seems to assume that delete works.
Yes, I ran a test and noticed that my memory got gobbled up pretty quickly. Drat!!! ...The problem is not merely in delete(), because delete just calls free(). The problem is that free() doesn't seem to work.
Anyway, regardless of that I like your idea of having detachInterrupt() simply disable the pin from interrupting, rather than using the delete() operator. I am working on it doing just that.
attachInterrupt() will return -1 on error, 0 if the pin has already been added to the list (the pin will be enabled if it is called and had previously been created already), and 1 if a new pin is created.