Discussion on:

Implement a MouseExit event for VB6 controls

If you use this, test it carefully - I've had problem doing something very similar in the case when the mouse is moved very rapidly off the control - sometimes the surrounding object which detects the mouseexit doesn't trigger the mouse event. In the end I had to check with pretty much all the background objects on the form (including the form itself) to reset the mouseover status

That's it in a nutshell. Most people move the mouse WAY to fast for a mere two or three pixels in a frame around a control to catch it's own mouse_move event. A better way is to use an API event capture to catch the global mouse_move event and, if the global boolean is true, check it's X,Y loc to see if it's still over the control. If it's not, then call the Mouse_Exit function and set the global back to false.

This is not pretty and can add a lot of processing overhead, so I don't suggest it as a viable alternative, but it's the only way I've found that always works.