I've had a look through the Mental Ray material library to see if there are any V-Ray maps or materials lurking there and I can't see any, so it sounds to me like it's using the V-Ray library for some reason.
In the library browser it might be worth changing the Materials>Using
value from "automatic selector" to "Mental Ray" and changing On Duplicate Material
to "replace from library" and re selecting the library item to see if it can force the correct material to load.
Let me know if that helps,