No way to intercept command-b or command-i on Mac WebKit HTML editors need to be able to tie in to do their own bold/italic handling (for notification change events or for recording extra data). Multiple HTML editing libraries @ Google have hacks around this bug. The current best-practice hack is to make the editable region plain-text only, and catch they key events yourself. You never see the key events if the editable region is full rich text.
Actually, I'm wrong. You can turn on read-write-plaintext-only, but then you still don't get any key events to catch.
Created attachment 30087 [details] test harness for showing this bug
The stack trace called: #0 0x0370985b in WebCore::executeToggleBold at EditorCommand.cpp:977 #1 0x03705d67 in WebCore::Editor::Command::execute at EditorCommand.cpp:1480 #2 0x0031f6fb in -[WebHTMLView executeCoreCommandByName:] at WebHTMLView.mm:2358 #3 0x0030f463 in -[WebHTMLView _handleStyleKeyEquivalent:] at WebHTMLView.mm:4121 #4 0x003148b3 in -[WebHTMLView performKeyEquivalent:] at WebHTMLView.mm:4134
*** This bug has been marked as a duplicate of 18693 ***