Why is the copy constructor not called?

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Whenever a temporary object is created for the sole purpose of being copied and subsequently destroyed, the compiler is allowed to remove the temporary object entirely and construct the result directly in the recipient (i.e. directly in the object that is supposed to receive the copy). In your case

MyClass MyObj(MyClass(1, 2));

can be transformed into

MyClass MyObj(1, 2);

even if the copy constructor has side-effects.

This process is called elision of copy operation. It is described in 12.8/15 in the language standard.

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