OBookmarkContainer actually re-uses the reference count of
ODatabaseSource, so converting ODatabaseSource::m_aBookmark to Reference
created a cycle, which somehow causes the dataloss, because evidently
something as important as storing the data must be done in the
destructor.

(regression from 2660d24a)

Change-Id: I4cad01dc9cdaf405c1eb31d6c0e161eb6712b78f