I understand that a convex function can not be maximized as there is no such value. However, consider the following function:

$$\begin{array}{ll} \text{maximize} & 3x^2 + 5y^2\\ \text{subject to} & x+y=12\\ & x,y\geq0\end{array}$$

But executing it in CVX and Matlab I get the following error: 

```
Disciplined convex programming error:   Cannot maximize a(n) convex expression.

```

But as I have specified the boundaries, should I not get some maximized value in this range?