Many users forget or even aren't aware of the fact that they can't have duplicate names for elements. Or in a long list of elements, they don't oversee which names are already in use. So they try to change the name, but it does not 'stick' (the name reverts immediately to what it was).
Of course it should be (or become) general knowledge and a good care that duplicate names won't occur, but just like with the prompt that warns for unallowed characters (spaces and all), it would be nice to prompt the user that there's a duplicate name. A small but helpful warning ?
I agree with you, Peter.
It is always a good idea to give meaninful unique names to elements or symbols. If you have several of the same then you can number them. Duplicating always add the word copy to the end.
I recommend to be very specific and not keeping generic names like rectangle or ellipse, etc...