I'm just upstreaming http://bugs.darcs.net/issue1513

It seems that if you use the roundup-admin interface to 'set
issueXXX,issueYYY nosy=+foo', this has the effect of applying the same
exact nosy list to both issues, and not the intended effect of
separately appending the user foo to both nosy lists.

Luckily, roundup made it very easy to automatically correct this
(nice!), but this sort of thing might bite others in the future.