The difference is that if you go to Applicants and type "man" in the quick search box, it will find all candidates whose name contains "man" but if you do that on the Placements screen, it will search Job Titles, Name, eMail address etc for those letters which is why you need to type the complete string you are looking for.
However, you can also just type the first few letters of the First name, and this will limit the list to contain the placements for applicants whose name begins with those letters - i.e. Cla would find Claire, Clare or Clariss.