I discover bug which appears as difference in page view and printing view.

Steps to recover this issue:

Make two two circle which are one over second with crossover paths
Select both
Execute "Object - Join objects" from menu.
Make object filled.
Result appears as with "Path - Merge" this same.
Print page. One object is not visible, second not.

Export page as PDF
Open file with AcrobatReader.
Result is as on screen.
Open file with Konqueror (Kpdf) or with gv.
None is visible.

Bertold