IMAP: Draft message composed offline is deleted when thunderbird is closed

Draft message composed offline is deleted when thunderbird is closed. There is no warning given to the user.

Steps to reproduce:
1. Setup IMAP account in Thunderbird
2. Compose message
3. File > Offline > Work Offiline (No Sync)
4. Write message
5. Save message
6. Close Thunderbird
7. Open Thunderbird

Result: Message lost.

Expected: One of the following two scenarios:
1) Save it to a local (On this PC) Drafts folder while offline.
2) Warn the user that teh data will be lost unless they save the file while online.

By searching I found that this affects other thunderbird users, therefore affects all platforms:
http://forums.mozillazine.org/viewtopic.php?f=39&t=702585&p=9542765
http://jonoscript.wordpress.com/2011/12/07/dear-thunderbird-i-know-you-cant-save-my-draft-please-stop-complaining-about-it/

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: thunderbird 11.0+build1-0ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-20.32-generic-pae 3.2.12
Uname: Linux 3.2.0-20-generic-pae i686
AddonCompatCheckDisabled: False
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 1.94.1-0ubuntu2
Architecture: i386
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: komputes 1951 F.... pulseaudio
BuildID: 20120313202109
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'Intel'/'HDA Intel at 0x90420000 irq 49'
   Mixer name : 'SigmaTel STAC9271D'
   Components : 'HDA:83847627,80862501,00100201'
   Controls : 45
   Simple ctrls : 25
Channel: release
Date: Tue Mar 27 13:25:10 2012
ForcedLayersAccel: False
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20120222)
IpRoute:
 default via 10.153.108.1 dev eth6 proto static
 10.153.108.0/24 dev eth6 proto kernel scope link src 10.153.108.150 metric 1
 169.254.0.0/16 dev eth6 scope link metric 1000
IwConfig:
 lo no wireless extensions.

 eth6 no wireless extensions.

 eth1 no wireless extensions.
ProcEnviron:
 TERM=xterm
 LANG=en_US.UTF-8
 SHELL=/bin/bash
Profiles: Profile0 (Default) - LastVersion=11.0/20120313202109 (Running)
RfKill:

RunningIncompatibleAddons: False
SourcePackage: thunderbird
UpgradeStatus: Upgraded to precise on 2012-03-23 (4 days ago)
WifiSyslog:

dmi.bios.date: 06/05/2006
dmi.bios.vendor: Intel Corp.
dmi.bios.version: MQ96510J.86A.0372.2006.0605.1717
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: DG965MQ
dmi.board.vendor: Intel Corporation
dmi.board.version: AAD37419-102
dmi.chassis.type: 2
dmi.modalias: dmi:bvnIntelCorp.:bvrMQ96510J.86A.0372.2006.0605.1717:bd06/05/2006:svn:pn:pvr:rvnIntelCorporation:rnDG965MQ:rvrAAD37419-102:cvn:ct2:cvr: