After updating to Snow Leopard (Mac OS X 10.6), I noticed an odd quirk in the Spelling Checker built into Mac OS X. This is the checker used by applications such as TextEdit and Stickies. Namely, the Ignore button in the Spelling and Grammar dialog is itself ignored. That is, when a word is flagged as potentially incorrect and I click the Ignore button (indicating that I want the word to be treated as correct going forward), the word continues to pop up as incorrect for the remainder of the document. This never happened to me under Mac OS X 10.5. This bug may not show up on all Macs running Snow Leopard, but it showed up on all three of mine.
After some investigation, I determined the cause: the Automatic by Language option. You’ll find it in the popup menu at the bottom of the Spelling and Grammar dialog. It’s the default selection. This is a new option in Mac OS X 10.6, replacing 10.5’s Multilingual item. Automatic by Language determines what language you are using and automatically shifts to the appropriate spelling dictionary. For whatever reason, it also appears to cause the Ignore bug. If I switched from Automatic by Language to U.S. English, for example, the Ignore function worked as expected.
A easily-solved related problem was that, each time I quit and relaunched an application such as TextEdit, the selection reverted back to the Automatic by Language default. To fix this, go to the Language & Text System Preferences pane. From the Text tab, access the Spelling pop-up menu and select U.S. English. This makes your selection the new default. Now the Ignore bug should be gone for good.
The remaining problem is: What should you do if you really want to use Automatic by Language? In that case, you’ll either have to wait for a Mac OS X Update that fixes the bug or learn to live with being ignored by Ignore.