Characters positioning with Cocoa backend

Running the chi.C macro with the Cocoa backend shows that Chi is misplaced in the Latex case. With cocoa the text extend returned for text before chi is to small. Of course it works well using the X11 backend. The OpenGL version also show an issue but in the opposite way compare to Cocoa.
Note that the same string drawn using TMathText does not show these issues.

The tlatex.C macro produce a misplaced exponent in the pdf file in case the Cocoa backend is used.