Manuel:
Yes, the brown cast is normal. Though it is easy to remove in LR using white balance, i made a color checker profile for the filter which works good as well. Most of the time the cast is quite pleasant on the warm side and i don't remove it completely. I prefer the BW filters instead of the Lee system with is good but bulky and has a strong blue cast.
Cheers
Werner
PS: Michiel how could you post your beautiful Pano in that big size?