Thumbnail images

Are the images displayed in thumbnail view mode for an MSOffice document (.xls, .ppt) dependent on the "save preview picture" option in the file (under File > Properties)? I'm getting inconsistent behaviour in my thumbnails and it's not displaying the image for certain powerpoint files.

Probably, yes. Opus doesn't generate these itself, they would be coming from a shell extension - where it gets them from I'm not sure.