The 3.1 branch had a bug that was crashing my X server (!), and I think I sorta fixed it. You can now post with it, too, but I haven't really done any major changes. I've been mostly working on LJ itself lately.
Technically, anything that crashes X is a bug in the X server - clients aren't supposed to be able to crash it. You might want to isolate the bug and report it to the X team (if you get some free time. :P)