When invoke-DSCbuild loads MyConfig, the command Import-DSCResorces -ModuleName MyConfig will cause an infinate loop loading the same same file over and over. In V4 it ignored the moduel file and just loaded the content of DSCResorce
I'm now in the process of seporating the MasterConfig from the composite parts more like the way the DSCbook works so I can get this to build on both V5 and V4.
v5 definitely has some changes, and we don't yet know if the current preview is the extent of those changes, or if there will be more by final release. You might want to wait a bit for final release before doing a lot of work on this.
It only takes a few minutes to make the changes. I move the folders from myConfig/DSCResorce to the root of in DSC_Tools and add a few more entries to Import-DscResource.
I did try a rename to make composite config fragments easier to find and discovered that there is a limit on the length of a module name. over 15 chars and it would fail to import. I don't know if this is a bug in the preview or if that was already that way in v4.
I will find out once I switch back to v4 latter this week.