Label missing after restoration

Initial situation:

• space A with label 'labelA' and 'de' (both labels are space labels and visible in space administration)
• space B with label 'labelB' and 'de' (both labels are space labels and visible in space administration)
• several pages in space B are labeled with 'de' and 'labelB'
  Now export / import:
• export of space B
• deletion of space B
• import backup file of space B
  Error situation
• after import of space B: the space labels are still visible in space administration (which is correct)
• after import of space B: pages, which were labeled with 'labelB' and 'de', are now only labeled with 'labelB' (label 'de' disappeared)
• the assignment of the label 'de' in the imported space B got lost on all pages, which had the assignment before

There is no effect on the other space A, which is correct. But the label 'de', which was used also in space A, isnt longer assigned to pages in space B.