The "Select Period" dropdown box of AWStats is created with all the months in the random order in Plesk 10.4.4.
Product issue #PPPM-44, which is fixed in Plesk 11.5.
There is the file which is named
nav.html. It is loaded in the frame in the AWStats home page. Its generation was broken until 11.5 and in the latest version it is fixed - sorted list of months is generated only after all logs processing.
So the solution here is to perform Plesk upgrade to the 11.5 version.