sort files - strange behaviour

Hi,
Sorting files with:

Tell application "Finder"
		set file_list to every file of source_folder whose name begins with "jda_to_telescope" and name contains "_09"
		set SortedFiles to sort file_list by creation date
		set thefile to item 1 of SortedFiles as alias
end tell

Works with 10.5.6 - I get the file with the latest creation date.
This doesn’t seem to work on a Mac with 10.4.11
I had to use reverse:

tell application "Finder"
	set file_list to every file of source_folder whose name begins with "jda_to_telescope" and name contains "_09"
	set SortedFiles to reverse of (sort file_list by creation date)
	set thefile to item 1 of SortedFiles as alias
end tell

Is this really related to OSX/Applescript version or could it be something else?

–Peter–