Simulink gets slower with every Simulation. How do I prevent that?

I'm using a quite complex model in Simulink. The pace of the simulation decreases with every Simulation. After restarting Matlab the pace of the simulation is back to normal.

Is this a known problem? If so, how can I prevent that?

[Niklas Nylén]

Check the memory usage in the Task manager (if you're using windows) and see if it increases every run. If you save data to the workspace each time the model runs the reason could be that less and less memory is available for the actual simulation.