The libertarian camp has always contained some folks who see themselves as "on the right" and others who reject that, either by saying "my heart is more on the left" or rejecting the dichotomy altogether. Before 9/11, those two groups could largely co-exist, except perhaps on the very fringes.
Since 9/11, and especially since Iraq, the distance between those two groups has grown much larger. Like an iceberg splitting in half and leaving two pieces floating on the water, and slowly drifting apart, the libertarian movement seems to be dividing over these issues.
An alternative hypothesis might be that those libertarians who were very comfortable seeing themselves as "right wing" or of "the Right" were more likely to have supported the war, while those who either reject that language and/or preferred to think of themselves as "on the left," were more likely to oppose it.
Of course, the "paleo" crowd might well be the counter-evidence here, as I think they tend to see themselves as comfortable on the right and have been staunchly anti-war, drawing on the very noble tradition of the Old Right.
Having always seen myself as having my heart on the left and very much rejecting the notion that libertarianism, or at least MY libertarianism, was "of the right," it is particularly stinging to be seen by others as a "defender" of the war, especially when I'm not.
If I'm right, and I may well not be, then the interesting question is why some libertarians are comfortable being "of the right" and others aren't, especially if the former is correlated with support for wars that cannot be justified on libertarian grounds.