If you sort the Length column, it seems to sort as Text, not as Numeric
How is your length-column defined? (Value, Sort by ..)
%_length% represents the formatted output - which is an alphanumeric string more or less.
To get a numeric treatment set these properties in the column definition:
sort by: %_length_seconds%
numeric: ticked.
Also see this fixed bug:
Thanks to all
The 'Sort By' works great
I didn't understand that field