Why application crash for "failed to resume" when using MFMailComposeViewController - objective-c

Question

My application need supporting user feedback through eMail. We prefer to use MFMailComposeViewController rather than url schema, because we need attaching some log files in the mail.
However application may crash for "failed to resume in time", when user act as follow steps.
1. Get into message editing view;
2. "Cancel-->Save Draft";
3. When saving draft, presh home button. Application will enter background state;
4. User launch application again, application will block in launch image. After few second, application will crash.
The device log said :
Jul 2 15:38:58 unknown SpringBoard[57] <Warning>: com.XXX failed to resume in time
Jul 2 15:38:58 unknown SpringBoard[57] <Warning>: Forcing crash report of XXX[461]...
Jul 2 15:38:59 unknown SpringBoard[57] <Warning>: Finished crash reporting.
Jul 2 15:38:59 unknown com.apple.launchd[1] <Notice>: (UIKitApplication:com.XXX[0x8c58]) Exited: Killed: 9
Questions:
Why my application block during resume?
Why MFMailComposeViewController use so long time to save draft?
How can I walk around to avoiding crash?
Crash Report:
Date/Time: 2012-07-03 09:25:40.222 +0800
OS Version: iPhone OS 5.0.1 (9A405)
Report Version: 104
Exception Type: 00000020
Exception Codes: 0x8badf00d
Highlighted Thread: 0
Application Specific Information:
com.XXX failed to resume in time
Elapsed total CPU time (seconds): 1.720 (user 1.720, system 0.000), 17% CPU
Elapsed application CPU time (seconds): 0.009, 0% CPU
Thread 0 name: Dispatch queue: com.apple.main-thread
Thread 0:
0 libsystem_kernel.dylib 0x35ca8010 0x35ca7000 + 4112
1 libsystem_kernel.dylib 0x35ca8206 0x35ca7000 + 4614
2 AppSupport 0x376c68c4 0x376b4000 + 75972
3 AppSupport 0x376c52f0 0x376b4000 + 70384
4 AppSupport 0x376c59a6 0x376b4000 + 72102
5 AppSupport 0x376c3cfc 0x376b4000 + 64764
6 AppSupport 0x376c3b8a 0x376b4000 + 64394
7 MessageUI 0x305dea90 0x305d5000 + 39568
8 MessageUI 0x306048b2 0x305d5000 + 194738
9 MessageUI 0x305f3914 0x305d5000 + 125204
10 MessageUI 0x305f2fa0 0x305d5000 + 122784
11 MessageUI 0x306025ce 0x305d5000 + 185806
12 UIKit 0x3727fcd4 0x37143000 + 1297620
13 CoreFoundation 0x33cf742e 0x33ce4000 + 78894
14 UIKit 0x371619e4 0x37143000 + 125412
15 UIKit 0x371619a0 0x37143000 + 125344
16 UIKit 0x3716197e 0x37143000 + 125310
17 UIKit 0x371616ee 0x37143000 + 124654
18 UIKit 0x37162026 0x37143000 + 127014
19 UIKit 0x37160508 0x37143000 + 120072
20 UIKit 0x3715fefa 0x37143000 + 118522
21 UIKit 0x371464e6 0x37143000 + 13542
22 UIKit 0x37145d26 0x37143000 + 11558
23 GraphicsServices 0x30578dec 0x30574000 + 19948
24 CoreFoundation 0x33d7154c 0x33ce4000 + 578892
25 CoreFoundation 0x33d714ee 0x33ce4000 + 578798
26 CoreFoundation 0x33d7033c 0x33ce4000 + 574268
27 CoreFoundation 0x33cf34d6 0x33ce4000 + 62678
28 CoreFoundation 0x33cf339e 0x33ce4000 + 62366
29 GraphicsServices 0x30577fc6 0x30574000 + 16326
30 UIKit 0x3717473c 0x37143000 + 202556
31 XXX 0x00002d26 0x1000 + 7462
32 XXX 0x00002ce4 0x1000 + 7396