Note in the original screenshot how the chevron in the terminal icon is lopsided (enlarged 400% in aa2.png), and the top edge of the disk icon at the bottom is jagged. Also, I've made aa1.gif (also at 400%), which shows when the security icon is hovered over, its gets a badly antialiased dark border. (The 256 color limitation of gif introduces its own artifacts, but the original problem is still clearly visible.)
Updating and rebooting trusty today did not help.
Note in the original screenshot how the chevron in the terminal icon is lopsided (enlarged 400% in aa2.png), and the top edge of the disk icon at the bottom is jagged. Also, I've made aa1.gif (also at 400%), which shows when the security icon is hovered over, its gets a badly antialiased dark border. (The 256 color limitation of gif introduces its own artifacts, but the original problem is still clearly visible.)