In a fresh odoo installation with demo data I have this strange behaviour:

• On a sales order, click edit

• The order lines can be moved and reordered via drag and drop (by clicking on the small dot on the left side). See picture 1:
  https://s3-eu-west-1.amazonaws.com/uploads-eu.hipchat.com/198549/2302468/u7r1fVZolGlBzwl/1.png

• Now, sort the table by clicking on a column header, for example 'price' as shown in picture 2:
  https://s3-eu-west-1.amazonaws.com/uploads-eu.hipchat.com/198549/2302468/jverzkYpvp0AVMm/2.png

• Now, drag & drop does not work anymore.

• Clicking 'save' and 'edit' again does not help.

• After reloading the page (ctrl-R), drag & drop works again.
  

A first short analysis shows, that the sort handler of the table somehow takes away the CSS classes needed for drag and drop (ui_sorting) from the table body. Before diving deeper, hopefully someone can explain this. Or is this behaviour wanted?