The problem is with 3.1.2.1 released today, using Google Chrome for Mac.
When I try to manually edit the CSS and JS list to be minified, I click on "Help" button, as on previous release. Well, when the popup window comes, I can select the JS and CSS files, but the bottom of the window has problems, because if I scroll to the bottom, I cannot see the "Apply and Close" button, so I cannot apply the file selection. I will revert to previous version until a serious upgrade and fix is released. What a mess. It's really sad, because I love this plugin, but these last two updates are a disaster.