Update Metadata: metadata assigned to wrong files

[jkm]

Under some circumstances, Update Metadata transposes values and metadata fields are assigned to incorrect files.

[xnview]

This problem has two requirements:
A. You must copy files inside XnViewMP, not in Windows Explorer
B. You must be in Details view

When you browse to a folder with new files for the first time in XnViewMP in Details View, exiftool metadata will not be properly imported, IF those files were copied from within the app.

SO, Continue the procedure above.
6. Remain in Details view.
7. Browse to the destination folder you created in step 2
8. You will see details for the files start to populate. Exiftool fields will populate for SOME files, but not all. The import process will be quicker than normal. The blue progress bar across the bottom might not appear.

Thanks to your detailed description I can reproduce the problem.