So, no one here uses <glossgroup>!
Ok. I have aforementioned <glossgroup>. In the ditamap I've added
<keydef href="glossary/ena.dita#a4a" keys="a4a"/>
Somewhere in the <topic> I use the <abbreviated-form keyref="a4a"/>. But when I open this topic later all information in the <abbreviated-form> is lost. The element is just empty.