I'm yet to check this due to being in the middle of live projects etc, but if you haven't already, it would be good to check the 'fixed' displacement is consistent across the different Chamfer modes in the Max Chamfer modifier, for example, Uniform, Radial, Patch, Quad etc.
What you choose here, currently has quite a noticeable effect on the displacement quality as I've just found out with the current stable release (Corona 6). Some real strange edge artifacts that become noticeable when opting for 'Patch' mode compared with 'Uniform' but sometimes you need to use the different modes and so it the displacement artifacts become unavoidable. It's worth noting this happens with both normal and 2.5D displacement.
Hopefully this has already been addressed and won't be an issue in V7 :)