Payload Alternate Paths Problems

Hi, I am a beginner mapper, and I currently making a payload map. I have problems when making the path_tracks. Here is a screenshot in Hammer

http://imageshack.us/photo/my-images/685/tf2payloadproblem1.png/

Logic_relay a_split_enable makes the cart follow the blue arrow, where a_split_disable follow the yellow arrow. The problems is when a_split_disable is triggered, and the cart recedes to path_a_34, it stops, and never move backward anymore. Even I kill path_a_s_7 , it still stops there. The cart recedes normally if a_split_enable is triggered. (forgive my bad English, if any)

Can anyone help me with this problem? Thanks

References:

path_a_33 have path_a_34 as Next Stop Target only
path_a_s_7 have path_a_34 as Branch Path only

a_split_enable
OnTrigger path_a_13 EnableAlternatePath
OnTrigger path_a_s_7 EnableAlternatePath
OnTrigger path_a_33 DisablePath

a_split_disable
OnTrigger path_a_13 DisableAlternatePath
OnTrigger path_a_s_7 DisableAlternatePath
OnTrigger path_a_33 EnablePath