Update of contribution via API changes status back to "completed"

If you update an existing, cancelled contribution via API (v3), the status gets changed back to "completed" unless you specify it explicitly.

Reproduced on current sandbox (4.4alpha1) with API explorer:
1. create new contribution with: trxn_id=test&contribution_status_id=cancelled
2. update the same contribution (modify transaction id) with: id=<the_id>&trxn_id=toast
3. observe that the status has changed back to "completed"
4. update the same contribution with id=<the_id>&trxn_id=toast&contribution_status_id=cancelled
5. observe that in this case the status is correctly set.

This might be "a feature, not a bug", but to me this behaviour doesn't seem right.