Why SImulink allows me to try and stream variable size signals ?

I have a variable size signal and I try to stream it (click signal and chose stream)

I get ofcourse the error :

Streaming of variable-sized signals is currently not supported. To eliminate this error, select the signal and then chose "Stop Streaming Selected Signals" from the Simulation Data Inspector toolbar menu.

What is more strange

"To eliminate this error, select the signal and then chose "Stop Streaming Selected Signals" "

What the hell ?

Why does Simulink allows me to do this operation anyway instead od throwing an error when i select to stream the signal ?

[Swarooph]

My guess is Simulink does not know the size of the signal until you update (Ctrl+D) or run the model.. Choosing the stream option is a static operation that can be done on any signal but that doesn't seem to trigger a model update (which is necessary to run a 'syntax' check on your model to determine signal sizes, parameter values etc).