Have you verified this e.g. with TTX, OTM, or another tool?
I could be wrong, but vaguely remember that 'aalt' is exported correctly when generating OTFs/TTFs with FLS5, but FLS5 creates a new aalt when importing OTFs/TTFs. So that what you see after importing to FLS5 is not what FLS5 exported ... (Curious for results of your check.)