More details on this. Chad H. pulled up the kernel source and it appears that there is specific code in net/ipv4/devinet.c when setting ip_forward that the accept_redirects field will be set opposite to ip_forward. Note that setting net.ipv4.conf.all.accept_redirects does not impact net.ipv4.ip_forward.
About the only reference to this behavior is the following: http://lists.openwall.net/netdev/2013/08/09/29
-Rob
scap-security-guide@lists.fedorahosted.org