1) What happened
Documentation does not show the types of the members (class, struct, enum)

2) How can we reproduce it using the example you attached
Version 4.1.2 still contains this information:
http://docs.unity3d.com/412/Documentation/ScriptReference/Bounds.html

But it was omitted starting (probably) at 4.2.0:
http://docs.unity3d.com/420/Documentation/ScriptReference/Bounds.html

In the linked example (Bounds), it's impossible to learn whether the member is a class or a struct. Classes are passed by reference in function and method calls, while structs are passed by value. It's important to realize what kind of member is being used.