Yes, it is. Unfortunately, there is no defined specification that details things like this in test frameworks. NCrunch's support for MSTest is emulated rather than integrated, which means that there is the potential for edge cases like this to be missed when providing support. These features are still very new in MSTest, so they haven't gone through the same rigorous real-world testing as other features.

I've noted this down to be investigated. For the time being, I recommend making sure you declare parameters as being of the same type as those specified on the method signature.