Hi S,
You don't have to complete the interaction when you confirm the partner. The interaction is completed when you end the interaction and that is the event when the interaction record is saved. Till then the interaction record is kept in edit mode in GDC.
You should find out which BTOrder is saved. I do not think it is the interaction record. It is possibly some other btorder initiated by your custom code.
Additionally, please check if you have an entry in table SMOFPARSFA for following parameter NO_DISTRIBUTION_LOCK_ON_SAVE