I'm using 7.0.8. exactly the way I used 6.3.9. before. :)
I try to explain.
In the entry field '% complete' (or so, I'm using the german version), I either manually enter a percent value or I use the arrow up/down keys on the right side of the entry field. In the old version it behaved like it should. When at 100% the task moved down into the 'completed tasks section', if <100% it moves up into the 'not completed tasks section'. In short, sorting is done when needed.
In the new version, if the value is 100% everything except sorting happesn. The tasks becomes grey, the COLUMN in the treeview shows 100%, but the sorting doesn't happen automatically.