[Bug] Video Settings Error(s) (Mac)

Summary: When changing the Overall Quality in my Video Options between Good and High, I experience an overall graphic "glitch" in the form of flat-colored pixels appearing on all buttons, tabs, bars, and drop-down menus.

Computer Information
Operating System: MacOS 10.5.8
CPU Type: Intel® Core™2 Duo CPU P8600 @ 2.40GHz
System Memory (GB): 4
Video Card Model: NVIDIA GeForce 9600M GT
Desktop Resolution: 1440x900
Hard Disk Size (GB): 232.57
Other Programs Running: Mumble, Firefox

Steps to Reproduce Bug
1) From the Options-->Video-->Graphics-->Graphics, select the Overall Quality drop down menu and switch from Good to High. Hit apply.
2) When loading screen is complete, repeat step but move drop down menu from High to Good. Hit apply.

What Happens Next: After switching back to an Overall Quality setting of Good, pixels appear throughout the game's UI, primarily in the top left of everything. There are no visual glitches within the game environment itself; only on my UI and interface options.

Additional Information: The visual error does not disappear when I use my hearthstone from Orgrimmar to Dalaran. Additionally, my Overall Quality shows as Custom, instead of good - though I did not edit any other options. I play at 1440x900(Wide) resolution in Windowed(Full Screen) mode.