Simulation (step thru) of Sequence Diagram?

[rhtt]

Hi, I've read the doc and can't see to get a Manual or Interpreted simulation (click through) of my sequence diagram to work properly. I drap classes onto the seq-diagram, connect them with messages/calls to operations, set breakpoints etc., but when I click "run" in the simulation window I first get a grey screen and when I hit "single step" the simulation is already done (according to the output in the simulation window). It looks to me like the simulation starts, but then just blows buy all of my message/call connections trough to the end, ignoring breakpoints as it goes.

I am using Version 11, Software Engineering edition.

What am I missing? Additional info needed? THANKS!!

[rhtt]

... after some more testing: could it be that sequence-diagram simulations (click troughs) only work with lifeline-objects? I created the same diagram, and instead of using "linked" classes to receive messages, I used "lifeline" obects. The simulation step-through then worked. The problem with the lifeline ojects is that they create objects that I don't need. I have many sequence diagrams, and I would end up with thousands of lifeline-obects that I don't need. I'd  prefer to (re) use the classes (links) in the sequence diagram, AND, be able to walk-throgh it with a siumulation. Is this somehow possible? THANKS!