Why do ToolTip balloons flash or flicker sometimes?

Balloon style ToolTips may flicker if the mouse moves over the little pointed corner of the balloon. This is because the mouse is no longer hovering over the main window - it is hovering over the ToolTip itself. To prevent this behavior, you can use the TTF_TRANSPARENT flag in the uFlags parameter of the TOOLINFO structure. This flag will cause mouse events to be passed to the underlaying window as if the ToolTip was transparent.