Apparently, the version of barebox that is used in ptxdist is not compatible with bareboxenv-target.
I cannot say why PTXDist would enable a feature and not update the source to support it. It appears to be a bug. There is an explanation here.
You could try updating the Barebox installation version by:
- Updating the make file to include a new archive of source
- Updating the make file to include a new md5 sum.
- Update any patch files associated with barebox (This is the hard part).
- Rebuilding PTXDist and verifying it works.
Personally, I think this might be a long bunny trail and I am not going down that path unless I find a good reason to do so. Best of luck!