To reproduce:
- Add ribbon bar with a few buttons subscribe to ScreenTipNeeded event and show different text for each button.
- Collapse the tabs by clicking the collapse button, the expand a tab by clicking its name.
- You will notice that the ScreenTipNeeded event is not fired.

Workaround:
Create separate screen tip for each element:
RadOffice2007ScreenTipElement button2Tip = new RadOffice2007ScreenTipElement();
button2Tip.CaptionLabel.Text = "button 2";
button2Tip.MainTextLabel.Text = "button 2";

radButtonElement2.ScreenTip = button2Tip;