This is a brand new install of the latest WordPress I am testing using XAMPP on my computer.
In the admin Control panel > Design > Widgets, when you attempt to edit the text and RSS widgets, only half of the edit function box is visible. The left half including the change and remove buttons are not visible. If you left click on the blue heading bar you can grab the box and move it around and everything is visible. As soon as you let it go it jumps back into place and only the right half of the box is visible again.
What can be done to resolve this? Is this a bug?