When running an Action Wizard that saves/exports a group of PDF files as (single) TIFF files, the very first file will have a ".tiff" extension and the rest will be ".tif". This ONLY happens the very first time you run the Wizard. Subsequent runs yields all files with a ".tif" extension. This is repeatable 100% of the time. Again, this applies when exporting the entire PDF file to a single TIFF file, not the feature that exports all images to multiple TIFF files.