Exported ODT does not contain generated images for formulas

I have created a test page with attachment images and formulas. When I export to ODT, the attachment images are contained in the Pictures folder of the ODT zip archive, the generated images for formulas are not. The content.xml  references the attached images correctly, like for example:

<draw:image xlink:href="Pictures/100000010000032000000148AC40D1B1D5154461.png" xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad" draw:mime-type="image/png"/>

But the paths to the (missing) formula images seems to be wrong:

<draw:image xlink:href="../../../../../../../../../../xwiki/tmp/formula/document%3Axwiki%3AGleichungen%3Eseki.Gleichungen.WebHome/17e8477e769552c056048007c27f9c294dff25592df319199a70f77777eb8760" xlink:type="simple" xlink:show="embed" xlink:actuate="onLoad"/>

When I export to PDF, all images are included.

When I export to RTF, attached images are included, formula images are empty gray boxes.

Your help would be very appreciated!

Greets Holger