Behaviour if the same data appears in two different root paths

[zklaus]

Not quite sure whether to consider this a bug, but here is what happened to me:

I analyze CMIP6 data on jasmin as well as PRIMAVERA data. For that reason I have two CMIP6 rootpaths, one pointing to /badc/cmip6/... and one pointing to .../primavera/stream1/.... Now, some primavera is being published to esgf and with some delay shows up in the cmip6 folder, as well ad in the primavera folder. This confuses esmvaltool that stops with the message

iris.exceptions.ConcatenateError: failed to concatenate into a single cube.
  An unexpected problem prevented concatenation.
  Expected only a single cube, found 2.

What do you guys think about rather giving priority to the first entry in the rootpath list?
Or giving a better error message?

[jvegreg]

What do you guys think about rather giving priority to the first entry in the rootpath list?
Or giving a better error message?

I would go for giving priority, following the definition order in the config_user