I, as a user, expect that everything is copied, or I am notified it is not possible due to max field length limitation. So the new solution cut a message without notifying me. It can be a large form and I might not notice it.
My opinion is that a typical use case of “Copy - xxxx” usage is for a field that identifies the record. That means the user always decides on what the text is and it most probably totally differs from the original “Copy of xxx” text. So I don’t think the user could make a mistake. They will change the whole text anyway.
In any case the root cause of the problem is that the field is too short. The user should never get to the point of having the text cut off even when “Copy” text is prepended. If it happens, the field length should be increased.