I'm having some weird issues with tooltip that contains Japanese characters.
I have a toolbar with two buttons, one of the buttons (button A) contains Japanese text.
The other button (button B ) has a tooltip containing Japanese characters.
When mouseover on the button with tooltip (button A), the font of button B looks smaller.
But when mouseover on button B, the font size changes back to normal.
No, you're doing nothing wrong - it works fine in Safari@Mac and Firefox@Mac also. It can be some IE8-specific css problem, however, it doesn't make sense to me why mouseover on one button causes a problem with another button.