title: NSUserDefaults synchronize crash
body: <p>I have encountered a SIGSEGV crash in my ios app right after calling:</p>
  
  <pre><code>[[NSUserDefaults standardUserDefaults] synchronize];
  </code></pre>
  
  <p>This is the part of the crash stack trace right after the synchronize command:</p>
  
  <pre><code>CoreFoundation 0x31920232 CFCopyTypeIDDescription + 29
  CoreFoundation 0x3191cd41 &lt;redacted&gt; + 204
  CoreFoundation 0x31910815 &lt;redacted&gt; + 16
  CoreFoundation 0x3188e1ac &lt;redacted&gt; + 140
  CoreFoundation 0x3189d1ff CFDictionaryApplyFunction + 158
  CoreFoundation 0x3191c483 &lt;redacted&gt; + 282
  CoreFoundation 0x318b237f CFPropertyListWriteToStream + 138
  CoreFoundation 0x318b115d &lt;redacted&gt; + 296
  CoreFoundation 0x318b1031 &lt;redacted&gt; + 132
  CoreFoundation 0x318b03c1 &lt;redacted&gt; + 492
  CoreFoundation 0x318b01d1 &lt;redacted&gt; + 20
  CoreFoundation 0x318bb3ff &lt;redacted&gt; + 110
  CoreFoundation 0x318bb8fb &lt;redacted&gt; + 74
  CoreFoundation 0x3193cb3b &lt;redacted&gt; + 30
  CoreFoundation 0x3193d509 &lt;redacted&gt; + 32
  libdispatch.dylib 0x39bd54b7 &lt;redacted&gt; + 22
  libdispatch.dylib 0x39bd99f7 &lt;redacted&gt; + 30
  CoreFoundation 0x318c7045 CFPreferencesAppSynchronize + 312
  </code></pre>
  
  <p>This is a rare crash so I can't reproduce it, and my question is:</p>
  
  <p>What can cause such a crash? </p>