The Service Type joined to ticket contain Events with "Allow time reseting" field not selected.
The attribute "Allow time reseting" (evt.user_settime) allows the user (or system) to override the fire time (delay time) that is defined for an event.
For example, when users add an event to a Service Type, they can redefine the fire time for the event only if the user_settime flag is set.
Otherwise, the fire time defined in the event is used.
System allows the user to create the event with "user_settime" as 0, however system doesn’t allow such events to be added to the service type.
Once the service type is created with an event having "user_settime=1", it can be used inside any Service Type. If after the event assigned to service type now is changed to "user_settime=0", the problem is reproduced
The information can be verified via SQL query:
select sym from evt where user_settime=0
The events used in the Service Type should not be shown in the results of the query as it should have value=1.