No, you did nothing wrong. I believe that the issue here is simply a preference setting.
SQL Developer Data Modeler is amazingly customizable. There are preference settings at the application level, the design level and the model level.
At the application level, one of the things you can set is what you want SDDM to pay attention to when comparing a relational model to a database instance.
As you can see in the image below, one of these comparisons is case sensitivity.
From the help:
Case Sensitive Names in Compare Functionality: Controls whether the letter case in object names should be considered when comparing two objects
I suspect that unchecking this comparison will make it easier for you to keep things in synch.
Hope this helps