400 Bad Request error when using "%1" reference to argument in title field

I have set up a view that takes two arguments: taxonomy term name and node type. It works fine. But when I add a title by entering "%1" for the title in the first argument definition, it get the 400 Bad Request error when I try to save the view.
Here's the argument:
Type: Taxonomy: Term Name
Default: Display all Values
Title: %1
Option: 0
Wildcard: *

I also get the error when I use a "%" reference in the other argument definition. This looks like a views integration issue.
Thanks.