That is because you are missing an additional entry:
*\
As per the Help page on Filter Settings in the program (with Filters dialog opened, press F1 to access the contextual Help on the said topic), an entry "*\*.mp3" will only include mp3 files in the root folder and will unselect all child folders.
An entry to include all folders is required - so add "*\" entry into the Files/folders to copy filter section.
*\
As per the Help page on Filter Settings in the program (with Filters dialog opened, press F1 to access the contextual Help on the said topic), an entry "*\*.mp3" will only include mp3 files in the root folder and will unselect all child folders.
An entry to include all folders is required - so add "*\" entry into the Files/folders to copy filter section.