Fantastic question. I asked this myself, several years ago. Ostensibly, the difference is a matter of where one places the emphasis. As far as I am concerned--and most if not all post-leftists and post-anarchists would disagree with me--the two share similar concerns. A post-anarchist could conceivably argue that post-left anarchists are interested in traversing the fundamental fantasy of leftist anarchism and are thus beyond traditional anarchism. Post-left anarchists might argue that post-anarchists are interested in overcoming the dogmas, stale orthodoxy, the reification of revolt, of classical anarchism. However, post-left anarchism seems to concern itself primarily with anarchism as it has played out in the realm of politics - post-anarchism can go further because it is not exclusively concerned with the problems inherent to the left and to political philosophy. Post-anarchists are also interested in aesthetics, ontology, epistemology, meta-ethics, and so on and not necessarily as these are connected to political practice. Therefore, I believe that post-anarchism can include the post-left traversal but it does not necessarily have to, and yet, it can also go much further than a simple critique against leftism. The arrogant part of me would argue that only a post-anarchist could understand what is really at stake in post-left discourse. And yet the equally arrogant part of me would argue that only a post-left anarchist could understand what is really at stake in post-anarchist political philosophy (somebody tell the post-anarchists).
The trick is to overcome the caricatures that either side has of the other, including all of the argumentum ad hominem implied. One does not need to be outside of the academia to be a post-leftist nor does one need to be inside the academia to be a post-anarchist. In many ways, post-anarchism is just contemporary anarchism. It is difficult to talk about anarchism today without bringing into the discussion certain key ideas from post-anarchism. Post-anarchism has retroactively defined for itself a discourse in the same way that postmodernism (a la Lyotard) has retroactively grounded modernism. Post-anarchism is what is in traditional anarchism more than traditional anarchism and post-left anarchism is what is in leftism more than leftism - neither of the two are against traditional or leftist anarchism but rather work through the fantasies and ideologies at the base of them.
