Hi guys - I am using the latest and greatest 2010 Q1 release for SL 4, with a SL 4 project, and I am beset with this same issue for drill-down charts. Basically, I mouse over a chart area, up pops the tooltip, click the chart to launch the drill-down, and the tooltip stays on screen. The only way to remove it is to return to the previous chart and mouse over the location where the tooltip launched, or if you don't know that trick (or the original chart has been lost), F5.
Big drag. Any fix available?