ios - Accessing a core data NSManagedObject after resuming from background crashes the app -

i'm using core data , have found app crashing after resuming background. i've identified crash occurring inside block method body when try access property on nsmanagedobject subclass.

i have property holds reference nsmanagedobject subclass.

@property(nonatomic,strong) calitem *calobject;

to reproduce crash first need call child viewcontroller(noteviewcontroller) passing block (notetextblock).

noteviewcontroller *noteviewcontroller = [[noteviewcontroller alloc]initwithnote:self.calobject.note notetextblock:^(nsstring *notetext) {                     self.calobject.note = notetext;  //crashing here                 }]; 

then send app background , resume it. afterwards in noteviewcontroller i'll return message calling viewcontroller.

if (self.notetextblock) {  self.notetextblock(trimmedstring); } 

when block returns , line self.calobject.note = notetext gets executed app crashes.

so apparently can't put block on stack, quite , resume app , continue defined inside block ? or doing wrong here ?

edit:
*** terminating app due uncaught exception 'nsobjectinaccessibleexception', reason: 'coredata not fulfill fault '0xb253100 <x-coredata://c2304b7c-7d51-4453-9993-d33b9113a7a5/dtoday/p57>''

the block defined inside child viewcontroller:

@property(nonatomic, copy)notetextblock notetextblock; 

edit2
when set breakpoint on line crashes.
(lldb) po self.calobject
$2 = 0x0b4464d0 <dtoday: 0xb4464d0> (entity: dtoday; id: 0xb489d00 <x-coredata://c2304b7c-7d51-4453-9993-d33b9113a7a5/dtoday/p57> ; data: <fault>)

i'm using magicalrecord lib manage core data stuff.

- (void)applicationdidbecomeactive:(uiapplication *)application {     if ([nsmanagedobjectcontext mr_defaultcontext] == nil         || [nsmanagedobjectmodel mr_defaultmanagedobjectmodel] == nil         || [nspersistentstorecoordinator mr_defaultstorecoordinator] == nil         || [nspersistentstore mr_defaultpersistentstore] == nil         )     {         //coming background, re-init coredata stack         [magicalrecordhelpers setupcoredatastackwithautomigratingsqlitestorenamed:dbname];     } 

i not familiar magicalrecords, ...

this exception raised when have un-faulted (as can seen in edit2) object no longer (or never had) exists in store.
might happen in few cases:

1. another context has deleted store
   
2. you have inserted it, obtained permanent id and:
   ** refreshed it
   ** saved (but parent context), reseted parent, , refreshed object in current context (or imported fault main context), see objectwithid:

   ---

there might other cases i'm forgetting, or unaware of.

if describe stack structure, , object state/origin might able understand problem better