I have a multi-thread Qt program where the Qt sometimes give a warning:

Qt Code: 
  1. Type conversion already registered from type QPair<QByteArray,QByteArray> to type QtMetaTypePrivate::QPairVariantInterfaceImpl
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I have found the warning is from this Qt’s function:

Qt Code: 
  1. bool QMetaType::registerConverterFunction(QtPrivate::AbstractConverterFunction *f, int from, int to)
  2.     {
  3.         if (!customTypesConversionRegistry()->insertIfNotContains(from, to, f)) {
  4.             qWarning("Type conversion already registered from type %s to type %s",
  5.                      QMetaType::typeName(from), QMetaType::typeName(to));
  6.             if (f)
  7.                 f->destroy(f);
  8.             return false;
  9.         }
  10.         return true;
  11. }
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I have checked my own code, nobody is calling this function, so it must be inside Qt’s own function. Could any one give me a hint what’s causing this issue or which function actually called the above function inside Qt’s code. I am using Qt 5.3.2. I wonder whether this could be a Qt’s bug instead of mine?