Hi Robert
I had a similar challenge and seemed to get around it by first moving each file to a 'working' directory (Copy File task and remove original) and processing it from there. In the Copy File task I set:
FOLDER - {TRIGGER(Active,LastTrigger,File.Result.TriggerFolder)}
INCLUDE FILE MASK - {TRIGGER(Active,LastTrigger,File.Result.Name)}
And in the Copy Settings Tab, set:
DESTINATION FOLDER - {USERVAR(defcopyfolder)} (defcopyfolder is a user defined variable storing the path of the folder to copy to). Also, here is where you select the option to 'Delete file after copy'.
Then to process the file in subsequent tasks just reference {USERVAR(defcopyfolder)}{TRIGGER(Active,LastTrigger,File.Result.Name)}
No idea WHY it works but now, copying 10, or 20 data files in to the Trigger folder runs the job automatically for each file. It is a bit convoluted but it seems to do the job for me.
Good luck
Andy