When does ssGetInputPortSignal return NULL in mdlOutputs

Hi, from the Docs I got that if the InputPort is set to SS_REUSABLE_AND_LOCAL by ssSetInputPortOptimOpts I cannot use ssGetInputPortSignal inside of the mdlUpdate function, because the signal has already been used and is not valid anymore or whatever.

But I neither did set that flag nor do I try to call ssGetInputPortSignal from mdlUpdate. I built the CMex function using the FunctionBuilder Block and sourced the mdlStart and mdlInitializeSizes functions out because I implemented the strategy pattern to be able to change the input data type dependent on a value passed in as a parameter. Is that a problem? I don't know where to search, since I did not change the code that I sourced out.

Thanks and greets!