The plugins can reset themselves when there is a problem with the database. I've noticed that if I run a lot of large plugins, like All-in-one-SEO, XML sitemaps, GZIP and some others that WordPress runs out of memory in the middle of things and some plugins lose their settings.
Consider reducing your plugins or use a php.ini files to bump up the memory and execute time.
You can then uninstall the plugin, delete it, and install it from scratch to assure that the options were completely deleted and reset.
My Stop-Spammer-Registrations plugin is killing me because it uses a bit of memory and in some environments crashes unexpectedly. I am reducing the memory requirements and it is better.
This plugin uses practically no resources so I can safely blame the other plugins on your install.