I made a copy of the built-in Invoice AU-NZ skill. By default, it captures the Total field from a different location. I tried to train the system to capture it from the expected region, but it still grabs it in the wrong place.
Currently, in case the technology considers Total field found out-of-the-box to be detected confidently, it ignores the trained field location. It is planned to change this behavior in future releases of Vantage.
Workaround is to use Advanced Designer to create extraction rules for particular documents.