If you’re a stickler for pixel-level details, you may notice that, under Light, Medium and Strong font smoothing setting in OS X, light-colored text set on dark-colored backgrounds will look thicker than dark text on light background.
On the contrary, if you set your font smoothing to “Standard – best for CRT”, you’ll notice that both text settings look optically even.
(You can try out these settings by going to System Preferences → Appearances → Font smoothing style.)
So under Medium font smoothing, highlighted text on Mail.app mailbox menu should look thicker than normal text, like this:
But when Mail.app text rendering bug kicks in, the thickening no longer occurs. Note how both texts now look optically even.
It seems that, for a brief moment, Mail.app decides to switch to “Standard – Best for CRT” text rendering and make the text look optically correct, but behaviorally inconsistent with the rest of the operating system.
I may be wrong in this issue, but have anyone else had this problem?