Comint read-only-prompt

[JD Smith]

I maintain the Emacs programming mode IDLWAVE, and have previously
hacked up a comint read-only prompt with an advice to snapshot-last-
prompt.

I just compiled a CVS Emacs v22, and was pleased to find that there is
a new comint- prompt-read-only variable.  However, when I enable that
variable, I get the following non-desired behavior:

     1. At each prompt, I am warned "Text is read-only".
     2. All my input is echoed back to me (I use process-echoes).  

I thought my prompt pattern could be at fault; it contains a \r
character (which IDL throws in at odd intervals).  I changed it to
something simple, and get the same behavior.  I noticed that it works
fine in simple Shell mode, so I must have something mis-configured.

Any thoughts?

Thanks,

JD