Hi,
purchasing workflow (including contracts) are usually started by an event from the release strategy, not by the change documents.
If an event is raised which starts the standard workflow this means that the event customizing is active.
check:
- the event log - swel - (activation by swels) for behavior of the workflows (yours and the standard)
- just to make sure, check that you marked the linkage as active in swe2
- check starting conditions (if you added them)
- check that the same event is used to start the workflows
- check the event binding of your workflow