Last modified: 2010-05-15 16:03:40 UTC
When moving a user talk page to another title in the user talk namespace, the subpages are moved into the Project: namespace.
Fixed in r35870.
The previous code used "an atrocious hack" to bump subject & talk pages to the appropriate target namespace, which sent you to the wrong place if you were directly moving a talk page to begin with -- adding 1 to the talk namespace instead of to the base subject namespace.
New code is nice and explicit and picks the right one.