I'm trying to do some caching using VaryByParam AND VaryByHeader. When an AJAX request comes in I return a partial XHTML. When a regular request comes in I send the partial XHTML page with header / footer.

I tried to cache the page by doing:

[OutputCache( Duration = 5, VaryByParam = "nickname,page", VaryByHeader = "X-Requested-With" )]

However this doesn't work... if I do a regular request first then run the AJAX call I get the full cached page instead of the partial and vice-versa. Seems like VaryByHeader is being ignored. Is it because X-Requested-With is omitted on normal requests? Or perhaps it's doing VaryByParam OR VaryByHeader?

My obvious way around this is for AJAX requests to call a different method which only returns partial pages, however I'd like to avoid that if possible.

I'm using ASP.NET MVC 1.0 with the OutputCacheAttribute.