Critical Description
In the Contributions table (And other places where asset type icons are displayed), if you add an image to a wiki block, the icon show the image icon not the curriki icon.
Here is an example- http://next.dev.curriki.org/xwiki/bin/view/MyCurriki/Contributions?user=solodad
Notice that "Wiki Block Position "1"" and "Blank Content Block Position #2" are both wiki blocks but show JPEG icons.
It is not sufficient to use attachment to determine type. Check attachment if it is a source asset and is not a text type.