Major limitation for Glossary?

I get the following error message when I try to deliver my new book via the iTunes Producer.

could not parse OPS/glossary.xhtml: duplicate id: group-0-gen-attachment" at Book (MZItmspBookPackage)

I had the problem before but I thought it was a bug. Here is what Ifound out.

I have 170 items in my GLossary most of them with graphics.

single graphics and grouped graphics

Wen I delete all the grouped graphics, then the error message goes away. Does that mean I can have only single (ungrouped) images in my Glossary?

Or is there another reason, limitation?