BPM Module doesn't list service tasks

I created a process model with various service tasks and no user task. Unfortunately, after my process run, when I open the process instance, it doesn’t list the various tasks that were executed. In my other process where I have user tasks, the tasks are displayed. Is it the normal behavior?

Yes, this a normal behavior. “Tasks” table displays a related ProcTask instances. ProcTask instance is created for user tasks only. If you want to display some kind of detailed process execution log, then you can try, for example, to create “fake” ProcTask instances manually when your service is executed.
Having a “detailed log” functionality is a good idea. We should think about it.