Have you found the answer to your question?

Could you please elaborate more on your case setup? B.Cs., residual trends, max interface Courant number, max Courant number, and how tight you set your solving parameters for different equations and ...

was it a closed system (like a container) or an open one?

Fist of all it is a closed system. For de B.Cs. no more to say, this is a trivial matter. v=0, u=0 at the wall. It is all about the interface compression Cnew[ij]= 1/4*[Cij]+3/4*(C[i+1j]+C[i-1j]+C[ij+1]+C[ij-1])/4.

Cnew is the novel coef and C the old one.

Rho=Rho_fluid*C+(1-C)*Rho_gas.

If C=1 we have all fluid in the Control volume

If C=0 we have all gas in the Control volume

Okay I made a systematic study recently with OpenFOAM about the issue that you were talking about. And it seems not surprisingly, you will over all lose mass/vol. while you track the whole mass in the system. And the reason for this is that the equation which is solved for the interface (alpha advection) is of hyperbolic type and once you try to solve it with a dissipative discritization (Upwinding) it'll make minor errors in your alpha field resulting in overall misbalance of mass/vol. in your enclosed medium. Of course this is not noticed once you try to simulate an open case. Anyways, what is important is that you cannot avoid this dissipation in the solution of alpha because it has also a good side and that is "stabilization". The good news is refining the cells at the interface would make this effect less vibrant.

BTW check the implementation of VOF in OF as well (interFoam solver) regarding the interface compression...

That's right, we gain in stability, we lose in interface sharpness, I prefer to code my own equations instead of using openfoam...

Refining the mesh means having a strong computer...

Thank's to you Dr. Hosein Heidarifatasmi