What is the name of the antipattern when a property changes value when assigned?

Question

C++ / C#

Code like this

public int Size { get { return _size; } set { _size = value + 15; } }<br/>

What is it called correctly? Thank you.

Answer 1

Not everything has a name, come up with a name yourself, like "Broken Phone".

Answer 2

What's wrong with changing a property with a setter?