I have two weird things going on with my SharePoint 2010 enterprise site when working with workflows in SharePoint Designer that might be related to each other. This site was migrated from 2007. The issues are within the same site collection. I've tried these steps in other site collections within the same farm and didn't have any issues.
1) In step one of my workflow that's being used on a basic list, I created "Start Custom Task Process". I then click on the "Task" link to bring up the Task Information window. There's an option to create new "Task Form Fields". When I click the "new" button to create a new field, I receive a dialog box that says "If this workflow has any running instances, changing this custom task may break those workflows". I click on "OK" the dialog box goes away and nothing happens after that. If I go back and click the new button again, nothing happens. I've attached a screenshot.
2) I tried to copy and modify the out of the box "Approval - SharePoint 2010" workflow at the root of my site collection. When I do, I get the dialog box to give the workflow a new name. When I give it a new name and click the OK button, the dialog disappears and my new workflow doesn't show up.