The latest version of Posts Widget includes a way to remove widgets from the Widgets page so it doesn't get cluttered with widgets you don't want to use. Unfortunately, removing them leaves a gap in the widget order, causing widgets on either side of the gap to get "stuck".

How to duplicate:

1. Click "Remove Widget Settings" in Admin -> Maintenance so we can start fresh.
2. Install Posts Widget
3. Go to Admin -> Plugin Settings -> Widgets and hover over the up/down arrows. Take note of the "order" parameter in the URL for each one.
4. Go to Admin -> Plugin Settings -> Posts Widget and uncheck "Posts Widget Day" and save.
5. Return to the Widgets page and check the order numbers. You'll see a gap in the order numbers where "Posts Widget Day" was.
6. Try moving the plugins on either side of the gap. They won't move up or down across the gap.

Needed fix: refresh the widget order after enabling/disabling widgets in Posts Widgets.