post method or request flattening array of hashes in params

Hi -- I have the following code in a cucumber feature:
http://pastie.org/752061
The problem is that the post method (or the controller) is flattening
the array of hashes into an array containing all the key-value pairs in
one hash, like so: http://pastie.org/752067
(Obtained from a call to inspect on params[:upload_data] in the
controller.)

I also call the post action from a controller spec with this code, which
is basically identical: http://pastie.org/752070
This treats the params correctly, and the inspection from this is:
http://pastie.org/752079

This is very weird!
I'm using the latest stable version of Rails, and Ruby 1.9.1
Can anyone shed any light on what may be going wrong, here?
Thanks,
   Doug.