Digital BW, The Print

In my continuing struggle to get neutral b&w prints from my Epson 
2200 I accidently discovered that on light-weight photo paper and on 
the wrong side (the less-white, coarser side)of heavier weight matte 
paper, the prints are quite neutral.  On the right side of the matte 
paper they have their usual magenta cast.  What is happening here?  
Does this mean that there may be a particular matte paper on which 
the Epson will print neutral blacks?  Is it a function of ink 
absorption?   Edward