"could not open cf_lock.lmdb" on heavily loaded hub on FreeBSD

After upgrade from 3.5.3 to 3.7.2(lmdb 0.9.17) at FreeBSD 9.3 amd64, I have seen strange errors in top.

cfe 3.5.3 does not generate this errors.

top -m io :

ast pid: 47991; load averages: 0.81, 0.58, 0.58 up 0+04:23:44 14:17:28
58 processes: 1 running, 57 sleeping
CPU: 8.3% user, 0.0% nice, 3.4% system, 0.1% interrupt, 88.2% idle
Mem: 157M Active, 7187M Inact, 687M Wired, 86M Cache, 1307M Buf, 7726M Free
Swap: 16G Total, 16G Free

PID USERNAME VCSW IVCSW READ WRITE FAULT TOTAL PERCENT COMMAND
48093 root 29 1 0 16 444 460 91.82% cf-agent
41735 root 772 1 0 29 12 41 8.18% cf-serverd

Only cfengine processes generate this fault errors.

What can it be and how to avoid or fix them ?