Crash in TextInput - how to debug?

I get crash reports for my iOS application with the following or similar stack in a broken topic:

0   TextInput                           0x0003149a TIInputManager::apply_case_changes_to_result(std::vector >&, KB::Hashmap const&, std::vector > const&) const + 402
1   TextInput                           0x00030bf3 TIInputManager::lookup() + 863
2   TextInput                           0x000307ad TIInputManager::autocorrection() + 61
3   TextInput                           0x00042d21 -[TIKeyboardInputManagerZephyr autocorrection] + 137
4   UIKit                               0x0011a319 -[UIKeyboardImpl generateCandidatesWithOptions:] + 377
5   UIKit                               0x00133071 -[UIKeyboardImpl addInputString:fromVariantKey:] + 2597
6   UIKit                               0x00130f8d -[UIKeyboardImpl handleKeyEvent:] + 1453
7   UIKit                               0x001308b7 -[UIKeyboardLayoutStar sendStringAction:forKey:isPopupVariant:] + 487
8   UIKit                               0x0012f3ad -[UIKeyboardLayoutStar touchUp:] + 3101
9   UIKit                               0x0012e737 -[UIKeyboardLayout touchesEnded:withEvent:] + 387
10  UIKit                               0x000165f9 -[UIWindow _sendTouchesForEvent:] + 525
11  UIKit                               0x00003809 -[UIApplication sendEvent:] + 381
12  UIKit                               0x00003123 _UIApplicationHandleEvent + 6155
13  GraphicsServices                    0x000065a3 _PurpleEventCallback + 591
14  GraphicsServices                    0x000061d3 PurpleEventCallback + 35
15  CoreFoundation                      0x00097173 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE1_PERFORM_FUNCTION__ + 35
16  CoreFoundation                      0x00097117 __CFRunLoopDoSource1 + 139
17  CoreFoundation                      0x00095f99 __CFRunLoopRun + 1385
18  CoreFoundation                      0x00008ebd CFRunLoopRunSpecific + 357
19  CoreFoundation                      0x00008d49 CFRunLoopRunInMode + 105
20  GraphicsServices                    0x000052eb GSEventRunModal + 75
21  UIKit                               0x00057301 UIApplicationMain + 1121
22  MyApp                               0x0000294b main (main.mm:8)

Only the bottom line ( main) belongs to me. It seems that the accident is somewhere in the touch event handler inside the text input frame, and this is due to auto-correction.

These crashes come with a dull consistency - it looks like a subtle bug, not iOS itself. The call stack is inconsistent - sometimes it ends in UIKit, sometimes in libobjc. However, the iOS version looks consistent 6.x.

Any idea how to debug this please?

EDIT: SIGSEGV / SEGV_ACCERR in stream 0. The error address changes - sometimes, zero, sometimes not.