Why does Embedded Coder preserve my tunable parameter inside TAN but not TAND?

I am generating code from a Simulink model in R2015a using the Embedded Coder target. I have a workspace variable a that is used in the model. I inline the rest of my values, but declare a as a SimulinkGlobal storage type so that it is not inlined in the generated code.

Where a is used in a constant or gain block, the parameter appears in the code. But if the constant or gain block has a value of tand(a), the numeric value of the expression is inlined in the code. This behavior does not occur if I instead use tan(a*pi/180).

It seems Simulink knows how to generate code for tan(a*pi/180) but not tand(a) and so defers to MATLAB to produce the numeric value, which Simulink then inlines.

Is this expected behavior? I see tand on the list of supported functions for code generation ( docsearch code generation supported functions ) and I would have thought that meant it was safe to use this way. Is there a different list of functions that support tunable parameters?