Not sure if anyone else is dealing with this problem, but I found this to fix the problem until Blizzard can solve it.

Source: http://forums.worldofwarcraft.com/th...00890683&sid=1

The crash happens when you mouse over different things in the game, in this case, the pumpkin to summon the Horseman. Whether your clicking it to summon him or not. This might also help on slaves to turn off the tooltip all together if you want to.

Original post:
Hey Guys,

There's tons of threads posted and lots of promising solutions. I have one that I've been testing for three days and have not had as much as lag spike when mousing over cogs. This works if you're willing to disable tooltips when you are anywhere a cog icon might show up.

You will need to create two macros, for "turn off tooltips" and "turn on tooltips".

Turn Off Tooltips
/script GameTooltip.Temphide = function() GameTooltip:Hide() end; GameTooltip:SetScript("OnShow", GameTooltip.Temphide);

Turn On Tooltips
/script GameTooltip:SetScript("OnShow", GameTooltip.Show);

This should get you through until the official fix comes down from Blizzard. Happy hunting!
People have said that this tooltip crash happens in different parts of the game, not sure how long it's been goin on, but this might help some out.