From the old Sivel.net support forum:
The titles are based on the title attribute of the link and not the image.
Is there a way to automate adding the title attribute to the a/link tag? It's a bummer that the title and alt text you specify in the media uploader are applied to the image and not to the link.
Oddly enough, if you insert a gallery, instead of a single image, the titles show up fine.
It would be really nice not to have to specify the title and alt tag on every post.