“Event’s position exceeds part’s boundary. Do you want to enlarge the part?”. Here, ticking the “please don’t ask again box” suppresses the message, but only until you close the project and open another one (or the same one).
Not sure if this is a bug (that’s been around as long as I’ve been using Cubase i.e. v6) or by design but personally think the message should be suppressed until you enable it again via a preference and I think that’s how most people assume it’s going to work.