The "Task name" in the case of the ServiceTasks is for internal use and cannot be changed. This value is internally used by the parsers, etc, to establish the type of service task. If this value is changed in the UI, when the process is saved, and opened again, it's not possible to know the type and the following error is produced.

1) Create a service task
2) Go to the task properties and set a random value in the "Task Name" e.g. "HelloWorld"
3) Save the process
4) Open the process
5) Click on the ServiceTask we'll have that
5.1) the task has no icon
5.2) but also the task properties like the task assignments, etc, are missing.

The attached screenshots shows hows what happens.