Documentation 
When you interconnect models, the operation and the properties of the models you are connecting determine the resulting model's properties. The following table summarizes some general rules governing how resulting model property values are determined.
Property  Expected Behavior 

Ts  When connecting discretetime models, all models must have identical or unspecified (sys.Ts = 1) sampling time. The resulting model inherits the sampling time from the connected models. 
InputName OutputName InputGroup InputGroup  In general, the resulting model inherits I/O names and I/O groups from connected models. However, conflicting I/O names or I/O groups are not inherited. For example, the InputName property for sys1 + sys2 is left unspecified if sys1 and sys2 have different InputName property values. 
TimeUnit  All connected models must have identical TimeUnit properties. The resulting model inherits its TimeUnit from the connected models. 
Variable  A model resulting from operations on tf or zpk models inherits its Variable property value from the operands. Conflicts are resolved according the following rules:

Notes UserData  Most operations ignore the Notes and UserData properties. These properties of the resulting model are empty. 