ALE mesh: free surface disturbed when moving

[tridelat]

When using ALE mesh, it seems that the free surface gets disturbed, particularly on the first few steps of moving the mesh. This can be particularly obvious when using MoveMeshMonitor as the mesh can move significantly from the initial step to the next step. This issue still occurs when waiting for a few time steps before moving the mesh. It also seems to stabilise after this initial disturbance (but the initial disturbance can cause the simulation to fail if the mesh movement/velocity is large).