The same as issue as posted below, though it does not appear solved even though it is marked as such: https://community.powerbi.com/t5/Desktop/Stacked-Area-Chart-Legend-amp-Tooltip-Order-Reversed...
rjhartop
Helper II
Helper III do see this as a bug to be honest - the tooltip should be in the order that it is in the chart - not the reverse.
Have taken your advice and created an idea here:
https://ideas.powerbi.com/ideas/idea/?ideaid=2a748865-164d-ec11-a3ee-281878bda47d