Map server crash (npctimer + unloadnpc)

(gdb) bt full
#0  0x081442a4 in ers_obj_free_entry (self=0xb7eb892c, entry=0x19)
    at ers.c:237
No locals.
#1  0x0809f534 in npc_timerevent_stop (nd=0xb32f8fa4) at npc.c:531
        sd = <value optimized out>
        td = <value optimized out>
        tid = (int *) 0xf25c9ec
#2  0x0809f728 in npc_settimerevent_tick (nd=0xb32f8fa4, newtimer=0)
    at npc.c:627
        flag = 244028040
        sd = <value optimized out>
#3  0x080c01ff in buildin_initnpctimer (st=0xb7eb9fac) at script.c:7497
        nd = (struct npc_data *) 0xb32f8fa4
        flag = 244028040
#4  0x080c57d6 in run_func (st=0xb7eb9fac) at script.c:2874
        i = <value optimized out>
        start_sp = 0
        end_sp = 3
        func = 161
        __FUNCTION__ = "run_func"
#5  0x080c604e in run_script_main (st=0xb7eb9fac) at script.c:3079
        c = 244028040
        cmdcount = 655312
        gotocount = 2045
        sd = (TBL_PC *) 0xf249070
        bk_st = (struct script_state *) 0x0
        bk_npcid = 0
        stack = (struct script_stack *) 0xb3c52b6c
        __FUNCTION__ = "run_script_main"
#6  0x0809f00b in npc_click (sd=0xf249070, nd=0x19) at npc.c:968
No locals.
#7  0x0806630c in clif_parse (fd=11) at clif.c:13017
        cmd = 144
        packet_ver = 22
        packet_len = 7
        err = 128
        sd = (TBL_PC *) 0xf249070
        pnum = 0
#8  0x0813a110 in do_sockets (next=50) at socket.c:743
        rfd = {__fds_bits = {2048, 0 <repeats 31 times>}}
        timeout = {tv_sec = 0, tv_usec = 41000}
        ret = 0
        i = 11
#9  0x08138b96 in main (argc=1, argv=0xbf97e8d4) at core.c:254
        next = 244028040