I'm currently migrating DearDrum.org Desktop to flex 4. Using an embedded font for the main navigation buttons; which are used to switch between states. When you're in a specific state the nav button for that state switches to a "selected button" skin which is just a copy of the regular skin with a few colours changed. The reason for doing that instead of just disabling each nav button in its given state is so they stay interactive, and are used when in the state to refresh/reload the state.

This worked fine but now in it's spark implementation when moving between random states the button label if it contains a single space will occasionally jump around - providing you've rolled over the button before changing state. It would take a boring while to explain it in more detail so I just recorded the behaviour. Best watched in full screen.