Description:
vim segfaults when using C-o(provided by clang complete/omnicppcomplete), and C-n to skip several items.

Additional info:
* package version(s)
local/gvim 7.3.918-1
local/vim-clang-complete 2.0-2

* config and/or log files etc.
output of gdb bt
-----------------------------------------------------------
Program terminated with signal 11, Segmentation fault.
#0 0x00007f2f693004b7 in kill () from /usr/lib/libc.so.6
(gdb) bt
#0 0x00007f2f693004b7 in kill () from /usr/lib/libc.so.6
#1 0x000000000051d25c in mch_exit ()
#2 <signal handler called>
#3 0x0000000000442bd7 in ptr2cells ()
#4 0x00000000005212b2 in pum_redraw ()
#5 0x00000000005440e8 in update_screen ()
#6 0x000000000048715e in ?? ()
#7 0x000000000048fe73 in do_cmdline ()
#8 0x0000000000467b2e in ?? ()
#9 0x00000000004684d0 in ?? ()
#10 0x000000000046c37c in ?? ()
#11 0x0000000000470177 in ex_call ()
#12 0x000000000048fe73 in do_cmdline ()
#13 0x00000000004a47d5 in ?? ()
#14 0x00000000004a4c4a in apply_autocmds ()
#15 0x000000000058d4bf in ?? ()
#16 0x0000000000521f24 in pum_display ()
#17 0x000000000044b288 in ins_compl_show_pum ()
#18 0x000000000044ff7e in ?? ()
#19 0x00000000004541ae in edit ()
#20 0x00000000004f6dac in ?? ()
#21 0x00000000004f6fb6 in ?? ()
#22 0x000000000050223a in normal_cmd ()
#23 0x00000000005bb15d in main_loop ()
#24 0x0000000000437c27 in main ()
-----------------------------------------------------------

Steps to reproduce:
0. If using omnicppcomplete, build the needed tags.
1. Go into a project(in my case, btrfs-progs)
2. Vim some file(in my case, cmds-check.c)
3. Type 'pr' in edit mode just before the retrun in cmd_check function,
and use C-o to begin a completion.
4. Use C-n to skip item.
(In my case, when the item is going to prune_one_block, the vim crashed)

P.S:
I also tested on my work desktop using omnicppcompletion,
the bug happens when try to use C-o and C-n to skip to the 3rd item.
And the bug happens and is more frequent than using clang-complete.