So you’re using or just installed the WordPress plugin “Contextual Related Posts” and it’s not saving your settings like thumbnail size etc?
There’s one easy solution
You have to scroll down on the related posts plugin settings page and search for “custom style” here you have to uncheck the default CSS style.
Now there’s still a problem, because it won’t though save your thumbnail settings. BUT there’s also a solution for that, because in the bottom on the settings page you have a field where you are able to put in your own CSS code. Now search with the help of Firebug plugin for the CSS name of the Thumbnails (mine was called .crp_thumb yours should be, too) and add your personal settings directly to the css code.
Now clear your browser cache and you now got alle the solutions to your problems.
Remove Contextual Related Posts from post page only show sidebar widget
You also can do that, on top of the settings page you finde some checkboxes where to show contextual related posts. Here you just uncheck everything and add your widget to the sidebar. Done