WstxParsingException when using .storageToHtml

[Alexander Junkermann]

When rendering a field (icon) of type "Storage Format" in a Plan View as following

<td>[entry.smCollection.icon.storageToHtml]</td>

this leads to the following error depending on the storage format stored in the field: 

Error: com.ctc.wstx.exc.WstxParsingException: Unexpected close tag ; expected . at [row,col {unknown-source}]: [6,2098]

for the following content of "icon" (which seems to be correct from my perspective):

<ac:image ac:thumbnail="true" ac:width="25"><ri:url ri:value="/download/attachments/103177291/IOL"/></ac:image>

while using other content like:

 <ac:structured-macro ac:macro-id="30918bd4-93fd-4f88-bca4-d90d9dee2873" ac:name="status" ac:schema-version="1">      <ac:parameter ac:name="colour">Green</ac:parameter>      <ac:parameter ac:name="title">4: INTEGRATION DONE</ac:parameter>      <ac:parameter ac:name=""/>    </ac:structured-macro>

everything renders fine. 

Any hints / ideas what I missed in the first example of content which could trigger the parse error?