Hi there,
if found a little bug while using the blend material. When assigning a Blend Material there is no possibility to view the Mask- Map in the Viewport. I have to connect the mask to any slot of Material 1 (Value 0) to make it visible.
If there is a Blend Material connected to my Blend Material I even have to assign a new material with this my Mask- Map to make it visible and change it back after scaling UVW.
Greedz :)