If you're doing a directory restore and that disables DAR, then there may not be a record within NBU. It pushes only the name of the directory to the NDMP host and expects it to match. The server isn't necessarily told which files were seen.
In your restore logs (at the beginning), do you get a message about DAR being enabled or disabled?
Depending on the NDMP server in use, you may be able to turn on more verbose logging and see things there, but that wouldn't be a generic solution across all servers.
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Darren