Using Watermark WP Image Protect Lite version 2.3 and WordPress 3.6.1.
Some of the images were exempted from watermark by me which does appear to be working. This weekend, I was looking at my site on a friend's iPad who has never browsed my site before. The watermarking was random for those images that are all supposed to have a watermark. Some postings and pages are not showing watermarks at all, yet others are working. I will continue to check. Maybe it's a device issue.
On a different note, when I found the plug-in was not working, I deactivated and removed it, yet then I could see no images at all in my image library. Just a blue question mark box for each image. I had to reinstall the plug-in in order to see my images again. Didn't seem to be a clean un-install.