layers not being calculated in displacement??

[mattblockhead]

Hey, I have been having a strange issue. 

when exporting displacement maps, layers are being ignored. It seems that at some point in the process an error has occured and layers made after that point are missing from the output. Everything else is working fine and the layers work fine in every other way.
I should also note that this happened on a previous project also. The only way around it I could fine was to export the final high res mesh and rebuild the levels in a new scene, which isn't a practical solution for doing WIP's

Does anyone have any idea what is going on???

Mudbox 2014 x64 - PC