Look at your urlconfs, find which urlpattern invokes your view Y and see if the regexp is more general than it ought to be. Try to comment out the urlpattern which causes the false match and see if it correctly matches X.
Typically, this is not a problem for me, but it does occur. Always keep more specific patterns before general ones. Use static prefixes to divide your url namespace, to prevent false matches.
You can assume, that it goes through the urlpatterns from top to bottom and the first one that matches will be executed.
As you know which view is executed (Y) think about that:
Y is before X: the patterns of Y matches the url (but shouldn't)X is before Y: the patterns of X doesn't match the url (but should)Can you provide some more explicit examples of your URLConf? Than I can give you a more explicit answer.
I would comment out the patterns in your url.py until you get a 404 error when you try to navigate to foo. If that pattern is an include, I would recurse down that and comment out lines in that url.py. Eventually you will know exactly which pattern is matching.
Then I would take the view function that it is calling and hard code that. If it is using a generic view or something subtle, I'd make it as obvious and direct as possible. At that point, you should know which rule is matching and why and what code it is executing in the view.