COMSOL Failing at Simple DE?

I've encountered a very simple problem with COMSOL's eigenvalue solver and I was wondering if anyone else has had the same problem.

I'm trying to solve the simplest DE imaginable. I'm trying to find eigenmodes for the 1D wave equation.

Governing Equation:
phixx = - lambda*phi

Domain:
x in [0, pi]

Boundary Conditions:
phi(0) = phi(pi) = 0

I'm using the eigenvalue solver in the General Form PDE module.

The solutions to this problem are sine waves. phi = A*sin(sqrt(lambda)*x), where lambda = n^2 for an integer n. COMSOL solves this problem fine.


The problem comes if I try to solve this problem by introducing an auxiliary field, beta.

Governing Equation:
phix = beta
betax = -lambda * phi

Domain:
x in [0,pi]

Boundary Conditions:
phi(0) = phi(pi) = 0

This should be an equivalent problem, but COMSOL is not able to solve it correctly. All of the modes it gives me look like garbage. Frankly, I'm beginning to distrust my previous results in COMSOL because of this issue...

Has anyone encountered anything like this before?

Any help would be appreciated,
-Julian