which hotspot to react the mouse click event

Hi all,
I'm just a beginner,and I need your help.
I have created a hotspot A ,it's url is a swf file，the swf is generated by a .as use Flex Builder.
In the .as file,I load an image and create another hotspot B，both hotspots can display well,but it's really strange that I don't exact know which hotspot will react the mouse click event,in my place,sometimes A react and sometimes B react.
I hope someone would tell me how can I fix which one to react,hotspot A or hotspot B?
many thanks.