After about 10 minutes I get:
2014-11-07T19:36:50.935-0500 I WRITES   [conn7] insert ycsb.bulk1 ninserted:1 keyUpdates:0 numYields:0  123ms
Segmentation fault (core dumped)

#0  0x0000000000000000 in ?? ()
WT-1  0x00007fe56cd6661a in __wt_compare (cmpp=0x7fe567bf37d0, tree_item=0x207b9a88, user_item=0x94efd48, collator=<optimized out>, 
    session=0x3f97400) at ./src/include/btree.i:1162
WT-2  __clsm_get_current (session=0x3f97400, clsm=0x642e4e0, smallest=1, deletedp=0x7fe567bf3840) at src/lsm/lsm_cursor.c:691
WT-3  0x00007fe56cd680fb in __clsm_next (cursor=0x642e4e0) at src/lsm/lsm_cursor.c:830
WT-4  0x00007fe56cd6d194 in __wt_lsm_merge (session=0x3f97400, lsm_tree=0x5255800, id=<optimized out>) at src/lsm/lsm_merge.c:311
WT-5  0x00007fe56cd725f8 in __lsm_worker (arg=0x3f90fe0) at src/lsm/lsm_worker.c:137
WT-6  0x00007fe56cac9e9a in start_thread (arg=0x7fe567bf4700) at pthread_create.c:308
WT-7  0x00007fe56bbd931d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:112
WT-8  0x0000000000000000 in ?? ()

$ rm -r /tmp/wt/*
$ LD_LIBRARY_PATH=$WT_INSTALL/lib ./mongod --storageEngine wiredtiger --dbpath /tmp/wt --wiredTigerCollectionConfig "type=lsm" --wiredTigerIndexConfig "type=lsm"
$ ./mongo
> use ycsb
> db.bulk1.ensureIndex({field0:1})
$ ./bin/ycsb load mongodb  -P workloads/workloada -p recordcount=1000000 -p table=bulk1 -threads 8 -s