web interface and command line dspam apparently failing to reclassify emails

When I click "As Innocent" or "As Spam" in the web frontend, the page
appears to simply reload, with no change in status for the email in
question. I picked apart the cgi and got it to tell me what command
it's running, which is as follows:

/usr/bin/dspam --source=error --class=spam --signature=22hexdigits
--user me\@mydomain\.com

When I run that command manually, it has no output and an exit code of
0. The email in question does not appear to have changed
classification, when I view the History in the web interface.

Is there some other way I should be checking the success of this
process, other than looking for the classification to change in the
web interface? If not, how can I find out what's going wrong here?

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