See http://netbeans.org/bugzilla/show_bug.cgi?id=183460 for details.
I was able to reproduce this issue without NB in the picture.
here is a quick sbs...
touch the file domains/domain1/docroot/wgfaSftCapture3.wmv
start the server
run the app attached to the NB issue... note the content type...
use the browser to open the admin gui
run the app attached to the nb issue... the content-type is different.