the problem lies with the protector,it is i belive silocone based,
Ive come across this a number of times,most recently on to of the same DFS suite,s
The first i cleaned in the normal way , and no big improvement, the second i did with M/S
I sprayed the whole suite with no2, then a mist of eco spotter,then brushed for ages!
the results were as far apart as you could get,
the second suite was clean, and the client happy,the first client was also happy,but i wasnt.
hope this helps,
dave