Ah, man, I even did a (apparently poor!) search before posting - thanks for the merge.
You can always take a look at the list of the confirmed bugs

But it's good to get reports for such stuff after patches, so that we can see if they've been fixed or not.
Edit: from some of these examples, this appears to happen when a river has two 'mouths.' I'll have to look for a river with two sources, though I think I recall those are ok
