Comment 2 for bug 312764

The documentation is a bit unclear about this, but you should end your command with a "." (dot). The dot is mandatory:

pet@workmate$ update-rc.d -n mysql start 99 1 2 3 .
System startup links for /etc/init.d/mysql already exist.

pet@workmate$ update-rc.d -n mysql start 99 1 2 3
Use of uninitialized value $level in string ne at update-rc.d line etc etc

I agree that the script doesn't handle it very well when the final dot is missing. This should be fixed. I suggest the patch which I attached to this bug (diff against 2.86.ds1-61ubuntu1 jaunty)

I'll create a debdiff shortly and ask someone to sponsor it into jaunty. Afterwards, I'll inform the Debian guys.