This behavior is tested for Nodes of the AnalogItemType which has further allowed behavior than a normal Variable. The important for this case is, that the AnalogItemType is usually only allowing values in a certain range. As NaN is really not a valid number it can never be in such a range, even not if the allowed range is the full range of the datatype. As a result the test case cannot be executed with such nodes but instead needs to be moved into the normal Monitor Value Change Conformance Unit where this test will be run with a normal floating point variable not having a constrained range.