Tab completion does not work for multiple words in the command window. (2013b, 2014b)

I have noticed that tab completion does not work after the first tab-completed word. e.g.:

fullfi<tab> --> fullfile

Works great, however, if I then use tab completion on a second word in the command (here trying for filesep) it doesn't work. e.g.:

fullfile([files<tab> goes to --> fullfile([files

This similarly doesn't work if I have a variable such as myFilePath in the workspace:

fullfile(myFile<tab> --> fullfile(myFile

With no tab completion. Paths, files in the current directory etc., do not work. I am currently running OSX 10.9 and am trying the 2014b prerelease, but have had the same problem with 2013a.