Treatment of sharp corners when using acoustic module

Hello,

I have a quick question which puzzled me a bit. For some time I was using Comsol's acoustic module to perform frequency analysis of the internal cavities. I always assumed that sharp edges in my geometry are sources of singularities, as such, I rounded them by introducing fillets with small radii. Recently, I tried two simple cases, one with fillets and one without. Surprisingly enough, both converged and produced almost identical eigenmodes and eigenfrequencies. I wander if Comsol uses certain approach to treat sharp corners, which is not explicitly documented?

Thank you in advance!