Why does the actionscript in movieclip autorun?

The situation is as follows:

on the staging, there are 30 frames and four layers, 1 at the bottom to 4 at the top.
layer 4 contains actionscripts at various frames number.
layer 3 are the frame labels.
layer 2 contains a movieclip that covers the whole duration of 30 frames.
layer 1 contains 2 moveclips, A and B, from frame 10 to 21, and from 21 to 30.

at Frame 6, i run some actionscript that use either gotoAndStop/gotoAndPlay to play moveclips A or B only.

However, when I skip moveclip A and directly jump to moveclip B, the actionscript in moveclip A will also excute.

Is this normal or a problem?

Please help. thanks

I am using flash CS3.
I have also attached the sample fla.