Hello Martin,
If i understand your design expectation correctly, when you click on 'create complaint' button from product overview screen, you want to navigate to complaint creation overview screen. Then user should be able to save the complaint.
If above is true, then you can have a look at the way standard SAP does.
Component - BT120S_CPL
View - BT120S_CPL/AdvSearchComplRL
event handler - EH_ONNEW
You may no longer get data loss pop up.
Hope above helps.
Thanks,
Kapil