This is a continuation of the work you helped me with in the post below.
The result is the PDF is correctly returned the first time, but not if the cache is used.
Sample project is below, with a failing unit test.
Found the solution myself, had to change the priority of the AddHeader attribute to always happen before the caching...
[AddHeader(ContentType = "application/pdf", Priority = -2)]
[CacheResponse(Priority = -1, Duration = 300)]
Please disregard question.