[Mono-list] Multiple simultaneous requests from same browser not executed simultaneous

[Marvin]

Hello,

Recently I found out that Mono/XSP will only process 1 request per
"user" at a time.
Here is my test case:
Clean MVC3 project with only a homecontroller with 2 actions and a
view for the index action. Code: http://pastebin.com/wRw1LEWi
The view for the index action is very as well: http://pastebin.com/SEyaUpq2

I would expect the webserver to process all requests at the same time
and respond them all after 5 seconds. This is what happens with the
ASP.NET Development Server. XSP however seems to be processing them
sequential, one at a time.
Here are my results:

dev server:
started at 21:32:49
finished at 21:32:54
started at 21:32:49
finished at 21:32:54
started at 21:32:49
finished at 21:32:54
started at 21:32:49
finished at 21:32:54
started at 21:32:49
finished at 21:32:54

XSP:
started at 21:34:47
finished at 21:34:52
started at 21:34:52
finished at 21:34:57
started at 21:34:57
finished at 21:35:02
started at 21:35:02
finished at 21:35:07
started at 21:35:07
finished at 21:35:12

I do however get the expected results when I call the slow action via
a sub-domain. This, of course, isn't allowed due to same origin
policy, I'd have to use JSONP or another workaround for this. But I
prefer not to use those.

Does anybody have the same problem, if so: what did you do about it?
My site relies heavily on async calls, some might take a bit long and
will cause the site not to respond.

Thanks in advance!

Kind regards,
Marvin