This happen when you're editing a template, or, if you're just adding it instead, once you add the parameter as well.
For example of very long names try to change Infobox settlement in https://en.wikipedia.org/wiki/Ames,_Iowa?veaction=edit .
Since some of these parameters only differ at the very end, like Fram noted, the user can be confused when seeing what is apparently the same parameter just repeated. Some of them also lack a description, so the description alone wouldn't solve the problem.
While he suggests that "a pop-up that displays the full name may be some initial solution", I think adjusting the character size or window size might work better.