Attachments created by import from xar file are not stored in file system

Our Xwiki (13.10.4) is configured with “store attachments in file systems”.
But if a XAR-file containing document attachments is imported, the attachments are stored in the data base.

Especially macros containing something like
will not work (and macros running in the operating system using the path too)

The attachments have to uploaded additionally.

Is there any additional configuration we have missed ?