Exciting news, maybe.
After over 100 trials, I noticed that a crash occured when I logged out
immediately after declining a guild invite. I was then able to cause the crash 4 times in a row this way. However, I'd also experienced 1 crash without seeing a guild invite. At the time, all of the Phanx* addons except PhanxBot and PhanxMod were enabled (I'd left those disabled since I thought they'd be more likely to be causing the problem, as they each do a lot of random stuff).
However, after further testing, I narrowed it down some more and found that
it only happens when PhanxTooltip (my private tooltip addon) is enabled. After a few trials, I realized that it was only crashing when there was a unit tooltip visible at logout. I was then able to reproduce the crash consistently that way, regardless of whether I'd seen a guild invite. I then tried enabling all addons
except PhanxTooltip and logging out immediately after declining a guild invite, and was not able to cause any crashes, so it seems the whole guild invite angle was just a big coincidence.
Edit:
Okay, I have conclusively identified the cause of the issue. The following test code will cause a crash on logout/exit, if a unit tooltip is visible, 100% of the time:
Code:
local f = CreateFrame("Frame")
f:RegisterEvent("CURSOR_UPDATE")
f:SetScript("OnEvent", function()
GameTooltip:Hide()
end)
Also going to report this on the Blizzard forums in case they feel like fixing it on the client end. Even if an addon is doing something "wrong" it shouldn't be able to hard-crash the client.
Edit #2:
Here is the official report in case anyone wants to follow it, and/or has more information to add:
http://us.battle.net/wow/en/forum/topic/4366253010