I am sure I came across this in the past with Cache and just saw this again in IRIS.

When rebuilding or swapping a DAT file for a database it retains the Resource of the DAT file, not the Resource of the Database it is being used for.

For instance, if I have a local Database called APP with a resource %DB_APP and I want to refresh the data from another Database called TEST that has a Resource %DB_TEST I can just copy the DAT file from the TEST folder to the APP folder.