Devise being logged out on post to different route

Im having a really strange problem with Devise. I have a route set up that accepts both get and post requests. On a get, it shows the form, on the post, it submits it.

When I send a post XHR to the route, when it gets there it tells me that I am not logged in, and sends me a 401 unauthorized. After that I have to log in, and then I can try again.

I have been trying to figure this out for hours, all I have been able to figure out is that my controller method is not getting called. I put in my own custom auth before filter, and it just confirmed that by the time my rails app gets called, the user is no longer logged in.

Also, if I open up the form, but dont submit it, I can continue on as normal. Somewhere in that XHR it is making devise log me out.

If you have any ideas please help, I have no idea what is going on right now...

Thanks

-Scott

EDIT: Adding relevant pieces of code

routes.rb

match 'projects/:p/filebox' => 'projects#show', :via => ["get","post"], :as => 'project_filebox'

projects_controller.rb

before_filter :authenticate_user! # <--- By the time this gets called, the user is logged out
def show
# ^^^^ Doesnt get called. Logger shows that it recognized route though
logger.debug "-----------projects#show"
logger.debug "Current user logged in:"+user_signed_in?.to_s

form that is being submitted

<form class="upload" action="<%= project_filebox_path(@project) %>?n=7&cType=<%= cType %>&fid=<%= fid %>" method="post" enctype="multipart/form-data">
    <input type="file" name="file" multiple/>
    <button>Upload</button>
    <div>Add / Drag Files To Upload</div>
</form>

Javascript that is uploading the XHR

formDataUpload = function (files, xhr, settings) {
            var formData = new FormData(),