Description of problem:
start guest with -no-shutdown,
Send 'quit' command via monitor, qemu-kvm core dumped with following info:
qemu: block/qcow2-cache.c:69: qcow2_cache_destroy: Assertion `c->entries[i].ref == 0' failed.

use qemu-img check guest_image got following info, the details pls refer to attachment:
77 errors were found on the image.
Data may be corrupted, or further writes to the image may corrupt it.
50461 leaked clusters were found on the image.
This means waste of disk space, but no harm to data.
30 internal errors have occurred during the check.
An error has occurred during the check: Success
The check is not complete and may have missed error.
ERROR OFLAG_COPIED: l2_offset=14 refcount=1
[stderr] ERROR l2_offset=14: Table is not cluster aligned; L1 entry corrupted
[stderr] Warning: cluster offset=0x1000000000 is after the end of the image file, can't properly check refcounts.

Version-Release number of selected component (if applicable):
kernel-2.6.32-251.el6.x86_64
qemu-kvm-0.12.1.2-2.251.el6.x86_64

How reproducible:
hard to reproduce, hit it only once

Steps to Reproduce:
0. boot vm with -no-shutdown
1. install a vm, poweroff it after installation
2. quit vm with monitor command 'quit'
  
Actual results:
qemu-kvm core dumped with "qemu: block/qcow2-cache.c:69: qcow2_cache_destroy: Assertion `c->entries[i].ref == 0' failed."

Expected results:
no core dump and work well.

Additional info:
1. Attached the full qemu-img log info.

2. Host info:
mem info:
# free -m
             total       used       free     shared    buffers     cached
Mem:         11776       6783       4993          0         69       5068
-/+ buffers/cache:       1646      10130
Swap:        16383          0      16383

cpu info:
processor	: 7
vendor_id	: GenuineIntel
cpu family	: 6
model		: 26
model name	: Intel(R) Core(TM) i7 CPU         920  @ 2.67GHz
stepping	: 4
cpu MHz		: 1600.000
cache size	: 8192 KB
physical id	: 0
siblings	: 8
core id		: 3
cpu cores	: 4
apicid		: 7
initial apicid	: 7
fpu		: yes
fpu_exception	: yes
cpuid level	: 11
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx rdtscp lm constant_tsc arch_perfmon pebs bts rep_good xtopology nonstop_tsc aperfmperf pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm sse4_1 sse4_2 popcnt lahf_lm ida dts tpr_shadow vnmi flexpriority ept vpid
bogomips	: 5319.07
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

3. cmd to boot vm:
qemu-kvm -drive file='RHEL-Server-5.7-64.qcow2',index=0,if=none,id=drive-ide0-0-0,media=disk,cache=none,format=qcow2,aio=threads -device ide-drive,bus=ide.0,unit=0,drive=drive-ide0-0-0,id=ide0-0-0 -device e1000,netdev=id2MZdQJ,mac=9a:6b:9f:a6:8e:67,id=ndev00id2MZdQJ,bus=pci.0,addr=0x3 -netdev tap,id=id2MZdQJ,fd=23 -m 6144 -smp 8,cores=4,threads=1,sockets=2 -drive file='RHEL-Server-5.7-x86_64-DVD.iso',index=1,if=none,id=drive-ide0-0-1,media=cdrom,readonly=on,format=raw -device ide-drive,bus=ide.0,unit=1,drive=drive-ide0-0-1,id=ide0-0-1 -drive file='rhel57-64/ks.iso',index=2,if=none,id=drive-ide0-1-0,media=cdrom,readonly=on,format=raw -device ide-drive,bus=ide.1,unit=0,drive=drive-ide0-1-0,id=ide0-1-0 -cpu cpu64-rhel6,+sse2,+x2apic -device usb-tablet,id=usb-tablet1,bus=usb1.0 -kernel 'vmlinuz' -initrd 'initrd.img' -spice port=8000,disable-ticketing -vga qxl -rtc base=utc,clock=host,driftfix=slew -M rhel6.3.0 -boot order=cdn,once=d,menu=off    -no-kvm-pit-reinjection -no-shutdown --append 'ks=cdrom nicdelay=60 console=ttyS0,115200 console=tty0' -enable-kvm