Consider a system of two bosons with spin, say photons. The wave function must be symmetric under the exchange of the two particles. For example, |psi> = |up> |down> + |down> |up> So far, so good. Now let us measure the spin of the particles, and let the outcome of the measurement be that the first particle is in the state |up> and the second particle is in the state |down>. If measurement induces the collapse, then after the measurement the wave function is |psi'> = |up> |down> However, |psi'> is NOT symmetric under the exchange of the two particles. Does it mean that the collapse violates the exchange symmetry?