Just tried this.
Tabbing goes from file to file, alpha-numeric according to name, regardless of how the list is sorted.
If you click open a folder, while in list view, the tab includes the contents that are listed, by name.
It's not random, but uses the folder/file name, regardless of how the files are sorted in the header.
The tab selects folder names first, then file names, strictly alpha-numeric, as they appear in the list. That's what makes the tabbing seem to jump around.