new → closed
In 1.6.x we trapped and discarded *any* errors thrown by an inline event handler. That is not good because it masks problems that the handler may have. We are trying to remove any of these omnibus try/catch situations in the jQuery code base to prevent that. So this error was occurring before, but just masked.
I think IE8 is justified in being upset that you're trying to set focus to an element the user cannot see or interact with. Most other browsers seem to ignore it since it's not a valid request, but there's no W3C guideline that I know of for what to do when someone asks to focus an invisible element. An error is probably better than silence when it comes to debugging.
If this is being caused by a plugin then the plugin should be fixed. Solutions include showing the element before setting focus to it, or using
.triggerHandler() if you just want to run handlers and not actually set focus.