over-release without a calltrace (using ARC), bad acces in main

I've recently converted to using ARC. However, i'm having a weird crash now, and the crashlogs are really unhelpful. During one of my application initialization processes (getting data from server, parsing it, setting up views), i get a bad_access. This is the error log from the device:

    Incident Identifier: 7CE05452-7C5D-424A-8529-AE7B17C9FEBC
CrashReporter Key:   b743ede30ce737293cf7444f67bb8a7b590c2fd9
Hardware Model:      iPhone3,1
Process:         BoreBeta [231]
Path:            /var/mobile/Applications/52A15437-459A-4160-95C4-BF5DF5C98C15/BoreBeta.app/BoreBeta
Identifier:      BoreBeta
Version:         ??? (???)
Code Type:       ARM (Native)
Parent Process:  launchd [1]

Date/Time:       2011-08-18 14:53:41.800 +0200
OS Version:      iPhone OS 5.0 (9A5288d)
Report Version:  104

Exception Type:  EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x80000004
Crashed Thread:  0

Thread 0 name:  Dispatch queue: com.apple.main-thread
Thread 0 Crashed:
0   CoreFoundation                  0x3758e380 CFRelease + 28
1   CoreFoundation                  0x375a93ec -[__NSArrayM dealloc] + 116
2   libobjc.A.dylib                 0x30a4e0be _objc_rootRelease + 30
3   libobjc.A.dylib                 0x30a4fdb0 objc_release + 32
4   libobjc.A.dylib                 0x30a4ee06 (anonymous namespace)::AutoreleasePoolPage::pop(void*) + 218
5   libobjc.A.dylib                 0x30a4ed22 _objc_autoreleasePoolPop + 6
6   CoreFoundation                  0x3759f050 _CFAutoreleasePoolPop + 12
7   Foundation                      0x337cd460 -[NSAutoreleasePool release] + 120
8   UIKit                           0x33b8d948 _UIApplicationHandleEvent + 6664
9   GraphicsServices                0x30ff8ef4 PurpleEventCallback + 876
10  CoreFoundation                  0x3760a9c4 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 32
11  CoreFoundation                  0x3760a966 __CFRunLoopDoSource1 + 134
12  CoreFoundation                  0x3760958c __CFRunLoopRun + 1364
13  CoreFoundation                  0x375ab036 CFRunLoopRunSpecific + 294
14  CoreFoundation                  0x375aaefe CFRunLoopRunInMode + 98
15  UIKit                           0x33b8b758 -[UIApplication _run] + 544
16  UIKit                           0x33b8898a UIApplicationMain + 1074
17  BoreBeta                        0x00002d8a main (main.m:14)
18  BoreBeta                        0x000027f8 start + 32

Thread 1 name:  Dispatch queue: com.apple.libdispatch-manager
Thread 1:
0   libsystem_kernel.dylib          0x3140d214 kevent + 24
1   libdispatch.dylib               0x376aaf60 _dispatch_mgr_invoke + 708
2   libdispatch.dylib               0x376aac7e _dispatch_mgr_thread + 30

Etcetera, i believe this is the only helpful part. When i let it crash from running in XCode, i see it crashes in main, and i don't get to see any calltrace, apart from main, UIApplicationMain and CFRelease on top..

In the past, i would look through my code for overreleasing objects, but i doubt this is the case because i'm now using ARC. How do you fix errors like this?

Edit: the code for parsing the data is on a seperate thread using GCD, and that's where my only @autoreleasepool lives.

Also, when running with NSZombieEnabled, i'm getting the NSArrayM release call. Unfortunately, that's the same we read in the crash log, so still no real progress here i'm afraid...

Edit: Ok. Once i fixed all my other memory errors without ARC, i got this error once again. So apparently it's not ARC-related...

Known bug introduced relatively recently.

Fixed in a future release (Note that Xcode 4.2 is under NDA, but llvm-commits is not). The commit message is available here. The commit message is slightly vague, but it should cover the case you are seeing -- if that is not the case upon the next compiler release (or you could build one yourself, if so motivated), please immediately file a bug and post the bug # here.