Mate most worn discs will rust a tad when left out in the rain. New ones don't seem to rust so quickly but over time they will.
I got EBC Pro-lites on my Track CBR and they rust terribly.
Not sure whats on the RR but when i ride to work in the rain 12 hours later when i get back on it the pads have stuck to the dics and rust starting to show already.
Let us know if you manage to find a solution.
Instead of lubing the discs with WD40 why not try grease which i here is as good.
I hope you were joking about the WD40 (i can see a compensation claim coming

)