I have the same problem (including all posts classed .even) on two very different setups, here’s what I’ve got:
Environment 1:
* WordPress 3.8
* bbpress 2.5.2
* CentOS (Linux)
* Apache / cpanel
* heavily customized theme loosely based on Twenty Twelve
* PHP 5.4.19
* tons of plugins, many custom, major ones include buddypress and w3total cache
Environment 2:
* WordPress 3.7
* bbpress 2.5.2
* Ubuntu (Linux)
* Apache (no cpanel)
* bbpress Twenty Eleven (a child theme of Twenty Eleven with small adjustments for better bbpress integration)
* php 5.3.10
* no plugins except w3total cache
Both sites have reply threading enabled.
