DSLR – Pentax Body

I noticed strage thing when i use UV, skylight filter or just though window with two glass sandwich (which stops UV) the AWB don’t work as good as it should, shots going to blue cyan tin especially when there is a lot of snow, but when i don’t use filters AWB works perfectly.Tried with different lenses; DA* 50-135mm, DA Limited 35mm and DA 10-17mm(tested though the window just to be суре it’s not the lenses) always same result.
Is this some kind of K20D sensors specialty?