Never seen that ! I use Grapher since 2007 and version 2.5 in Mavericks 10.9 & 10.9.1, Imac 21,5" and MacBook Pro : all correct.
Have you seen other anomalies in Preferences and all menus, Examples, Built-in Definitions ?
I know a possible remedy you could try : shut down and re-start your MacBook Pro.
You may also try another language than the usual one : quit Grapher, menu Apple, System Preferences, Language & Region, may be choice between "English“, “British English" and “U.S. English“ (I have also French because I set Mavericks in French), open Grapher in available languages and check Equation Palette.
Try the three ways to show the Equation Palette : 1) menu Window ; 2) keyboard shortcut Shift+Command+E ; 3) Button in the Equation Editor sub-menu Show Equation Palette.
Open the “Sums“ 2D Example from the menu Examples then call the Equation Palette
If you can't get an available equation palette, download the PDF file “Instructions for Use - Grapher“ on website (all free)
and use all keyboard shortcuts listed pages 51 and 52, chapter Expressions pages 41-48.
Menu Examples to copy and paste some special signs from these examples.
I can enter all signs of the Eq. Palette in 2D Grapher files, save them as .gcx files and send you these files by e-mail (my adress on last page of the website). It's possible to copy and paste elements from the equation editor of a Grapher window onto an other Grapher window, that means using Grapher files as equation palettes.
"Sursum corda" : your situation is not desperate !