I haven't really figured out what caused the problem, but I was having trouble with the way the curly braces showed up in Terminal.app, where the closing brace seems to get corrupted in drawing, as can be seen in the image at right. The problem only seems to occur in the 10pt variant of Monaco, as used by the Terminal. It goes away if anti-aliasing is turned on for the window, but within Terminal this has a negative impact on the legibility.

The workaround: In Terminal, go to the Window Settings, click on the pulldown menu to get to the Display settings and click on the Set Font button. You will get a standard font selection window. Now go to the Size input. Instead of selecting a manual size, go directly to the input box that reads the current point size (should be 10 or 10.0) and change it to 10.1. Problem solved.

Unfortunately, this solution does not work for iTerm, which seems to ignore non-rounded font sizes.

[robg adds: I couldn't reproduce this on my machines, but perhaps it will be useful to someone...]