Unexpected results from XAPI with bounding box

I’ve been trying to use the XAPI to give me a list of all the relations for bus routes in Oxford, UK. I’ve got the following call:


What’s returned seems to include a lot (probably all) of the routes I was expecting, but also several other relations (a lot from Germany) that don’t appear to be anywhere near the specified bounding box.

For instance, it also returns http://www.openstreetmap.org/browse/relation/81619 and http://www.openstreetmap.org/browse/relation/61335 and http://www.openstreetmap.org/browse/relation/61333

Does anyone have any idea what’s going on here, and whether I’m doing something wrong, the API is doing something wrong, or there’s some subtlety in how it finds relations for a given bounding box…?