Temporary fix for #809, until we can figure out the cause of the crash

@@ -317,7 +317,11 @@
     }
     }
     if (self.cancelBlock) {
     if (self.cancelBlock) {
         self.cancelBlock();
         self.cancelBlock();
-        self.cancelBlock = nil;
+        
+        // TODO: this is a temporary fix to #809.
+        // Until we can figure the exact cause of the crash, going with the ivar instead of the setter
+//        self.cancelBlock = nil;
+        _cancelBlock = nil;
     }
     }
 }
 }