X11 window doesn't take up whole screen in OS X Yosemite

Solution 1:

I had the exact same problem but on a very different Mac using very different X applications. Mine is a Mac Pro from 2011, running four monitors on two ATI Radeon HF 5770 video cards. Every X program that I tried had the same problem as you describe.

I did the upgrade to Yosemite on my MacBook, but the version of X was earlier (2.7.5 instead of 2.7.7). So I took the X11 on my Mac Pro down to 2.7.5 and then it worked on three out of four of my monitors (2.7.7 gave the problem on all four).

I ultimately erased the file ~/Preferences/org.macosforge.xquartz.X11.plist to reset the preferences, and this seems to have solved the problem entirely. I have not yet tried this out with the newest version of X11.