actually, we had a bug here that we have fixed with yuuvis RAD 7.8.
The additional comment will be written to the process history.
If model/activity is configured so that events are published (checking the "eye" on events in Logging section in designer), the event and the comment will be visible in client history, since client shows only the published events.
management studio shows all events, and contains complete history of a process.
Here is a screenshot how it looks like in mgmt studio:
("ac" was the comment I wrote in designer to indicate event "Activity Created"). Note that these extra comments cannot be localized and are more of a tool for making development of models a bit easier. So it is good practice to remove them from productive models and leave client do its magic :)