WT_REF structures freed while still in use

#0  0x0000000080159208 in __wt_ref_key (page=0xbb1dcdc0, ref=0x3ff4c00dee0, 

    keyp=0x3ff440a6a08, sizep=0x3ff440a6a10) at ../src/include/btree.i:706

#1  0x000000008015bd36 in __wt_row_search (session=0xbaed76e8, 

    srch_key=0x3ff440a68b0, leaf=0x0, cbt=0x3ff440a67b0, insert=true, 

    restore=false) at ../src/btree/row_srch.c:378

#2  0x0000000080205186 in __cursor_row_search (session=0xbaed76e8, 

    cbt=0x3ff440a67b0, leaf=0x0, insert=true) at ../src/btree/bt_cursor.c:385

#3  0x0000000080207bfc in __btcur_update (cbt=0x3ff440a67b0, 

    value=0x3ff440a68d8, modify_type=4) at ../src/btree/bt_cursor.c:1232

#4  0x0000000080208d62 in __wt_btcur_update (cbt=0x3ff440a67b0)

    at ../src/btree/bt_cursor.c:1485

#5  0x0000000080184708 in __curfile_update (cursor=0x3ff440a67b0)

    at ../src/cursor/cur_file.c:366

#6  0x000000008000e380 in row_update (tinfo=0xbb8e8490, cursor=0x3ff440a67b0, 

    positioned=false) at ../../../test/format/ops.c:1793

#7  0x000000008000bea2 in ops (arg=0xbb8e8490)

    at ../../../test/format/ops.c:1043

#8  0x000003ff907881f2 in start_thread (arg=0x3ff81fff910)

    at pthread_create.c:310

#9  0x000003ff905098da in thread_start ()

    at ../sysdeps/unix/sysv/linux/s390/s390-64/clone.S:76

(gdb) frame 0

#0  0x0000000080159208 in __wt_ref_key (page=0xbb1dcdc0, ref=0x3ff4c00dee0, 

    keyp=0x3ff440a6a08, sizep=0x3ff440a6a10) at ../src/include/btree.i:706

706			*sizep = ((WT_IKEY *)ref->ref_ikey)->size;

(gdb) p *ref

$3 = {page = 0xffffffffffffffff, home = 0x0, pindex_hint = 1023, 

  state = 1879626048, addr = 0x1204003030, key = {recno = 3472328330587879480, 

    ikey = 0x3030303830373838}, page_del = 0x2f4c4d4e4f505152, page_las = 0x0}

(gdb) printf "%s\n", &ref.key

00080788/LMNOPQR

(gdb)