Impossible delete qcow2 snapshot because 'device not found'

[mmenaz]

Hi, I tested with a VM (qcow2 image file format) and took at snapshot at "stage 0" before trying to install paravirt (virtio) drivers, so disk was IDE and not, after snapshot, is Virtio.
Since everything works fine and the snapshot is no more needed, I tried to delete it from GUI, but got the error:

task failed
VM 200 qmp command 'delete-drive-snapshot' failed - Device 'drive-ide0' not found

Now my questions are:
a) how can I force it? Now snapshot state is "deleted" but I still see it (because VM is still running?)
b) where are snapshot stored for qcow2 format? I've the feeling that they are inside the qcow2 file, so seems impossibile to just delete a "snapshot file" and the related <VM>.conf part
The only solution that comes to my mind is shutdown the vm, do a backup and then a restore, but will take long and I need the VM running

#IP 181, GW 15
agent: 1
boot: cd
bootdisk: virtio0
cores: 4
ide2: backup:iso/virtio-win-0.1.112.iso,media=cdrom,size=55592K
memory: 6144
name: Win2012R2CN
net0: e1000=36:30:37:38:66:38,bridge=vmbr0
net1: virtio=3A:33:33:36:31:66,bridge=vmbr0
numa: 0
ostype: win8
parent: predriver
smbios1: uuid=1302b073-03ef-4a46-bf2c-c3b75818d791
sockets: 1
startup: order=200,up=120
virtio0: local:200/vm-200-disk-1.qcow2,cache=writeback,size=80G

[predriver]
#before Virtio installation
bootdisk: ide0
cores: 4
ide0: local:200/vm-200-disk-1.qcow2,cache=writeback,size=80G
ide2: backup:iso/Windows_Svr_Std.iso,media=cdrom,size=5319016K
memory: 6144
name: Win2012R2CN
net0: e1000=36:30:37:38:66:38,bridge=vmbr0
numa: 0
onboot: 1
ostype: win8
smbios1: uuid=1302b073-03ef-4a46-bf2c-c3b75818d791
snapstate: delete
snaptime: 1451079546
sockets: 1
startup: order=200,up=120

 

[mmenaz]

Solved shutting down the VM and then removing snapshot. Is it normal or a bug?