Sometimes my request comes in as HTML and other times as TEXT/*. Why?

I have an AJAX upload action for my Rails app. Sometimes it comes in as:开发者_如何学编程

Started POST "/products/temp_upload" for 63.148.78.244 at Fri Sep 24 21:34:27 +0000 2010
  Processing by ProductsController#temp_upload as HTML

And everything runs smoothly.

Other times it comes in as:

Started POST "/products/temp_upload" for 63.148.78.244 at Fri Sep 24 21:49:35 +0000 2010
  Processing by ProductsController#temp_upload as TEXT/*

And I get a 406.

The only consistency I see is that it works on Windows and fails on OS X. Does anyone know why this is and how to fix it?

Thanks!

This means the browser making the request will accept all text response formats