From Triggers page:
Ack a trigger in Problem state (with one problem event) -> it will add the suffix.
Then click to "Acknowledged" and add additional ask -> this and all rest acks will be added w/o the suffix.
Why ?

Then generate OK event and ack the trigger in OK state (with one OK event) -> it will NOT add the suffix.
Again, why ?

It's inconsistent.

In my understanding the suffix should be added ONLY when we ack more than one events.
If we ack a single event - the suffix should not be added because it will not be true !

Then in most cases it will safe some space in database and alerts with corresponding macro will look a bit compact.