Never seen that in any version of Trainz: all wagons having the same running number (123456). Consist was: 1x<kuid2:532427:100027:2> + 3x<kuid2:661281:35120:2> + 2x<kuid2:661281:35119:2> + 1x<kuid2:661281:35120:2>.
Is that with Compatibility Mode in Trainz settings set to "Maximize Compatibility"?
If not, reset to that and check the ARN script behaviour after making the change.