System Information
OS: Windows 7 x64 (confirmed in x86 as well)
Graphics: ATI Mobilitiy Radeon HD 4200 series

Blender Version
Broken: 2.73
Worked: 2.68a

Short description of error
"Face selection masking for painting" button (next to layers grid on the bottom toolbar) would previously display a wireframe overlay over the active object in texture paint mode, as well as the other two painting modes. It no longer works in texture paint mode, but still works in the others.

Exact steps for others to reproduce the error
Open a new file. Take the default cube, subdivide it (for better wireframe demonstration), mark seams, and unwrap to a blank texture. Attach the texture to the default material and set UV mapping. Enter Texture Paint mode and click the "Face selection masking for painting" button. Cycle through the other paint modes for comparison.