Does the insertion operator make a copy of the value it is inserting?

For example... Lets say I have the following code...

Qt Code: 
  1. struct someStruct {
  2.     int x;
  3.     double y;
  4. };
  5.  
  6. QList<someStruct> testList;
  7.  
  8. void className::methodName()
  9. {
  10.     someStruct tempStruct;
  11.     for (int x = 0; x < 10; x++) {
  12.         tempStruct.x = x;
  13.         tempStruct.y = 0;
  14.         testList <<tempStruct;
  15.     }
  16. }
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tempStruct is local to the "methodName" method.
After this function returns, is testList valid?
In my test code it is. All works ok. But I'm trying to track down a particularly elusive bug and this is one of my concerns.

Here's a snippet of my actual code. I'll try to explain the error.

Qt Code: 
  1. LayerDef layer; // LayerDef is the struct definition       
  2.          if (line.startsWith("Original")) {
  3.             while (!line.startsWith(',')) {
  4.                 line = stream.readLine();
  5.                 if (line.startsWith(',')){
  6.                     continue;
  7.                 }
  8.                 tokens = line.split(',');
  9.                 layer.t = tokens[1].toDouble(); // layer is a struct.
  10.                 layer.dc = tokens[2].toDouble();
  11.                 layer.dlt = tokens[3].toDouble();
  12.                 layer.mlt = tokens[5].toDouble();
  13.                 layer.dcc = tokens[6].toDouble();
  14.                 layer.rp = tokens[7].toDouble();
  15.                 layer.name = tokens[8];
  16.                 layersOriginal <<layer; // layersOriginal is a QList (QList<LayerDef> layersOriginal;)
  17.                 if (firstPass) {
  18.                     firstPass = false;
  19.                     // Update slider values on first pass only.
  20.                     ui->sldT->setValue(layer.t); // Note this line.
  21.                     ui->sldDC->setValue(layer.dc);
  22.                     ui->sldDLT->setValue(layer.dlt);
  23.                     ui->sldMLT->setValue(layer.mlt);
  24.                     ui->sldDCC->setValue(layer.dcc);
  25.                     ui->sldRP->setValue(layer.rp);
  26.                 }
  27.                 ui->lstLayers->addItem(layer.name);
  28.             }
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This code runs ok. However, after it runs, any attempt to access sldT (a QSlider) causes an assertion failure.
The failure is "ASSERT failure in QVector<T>:perator[]: "index out of range", file ..\..\Qt\Qt5.3.2\5.3\mingw482_32\include/QtCore/qvector.h, line 385".
I've went through the code for QSlider and QAbstractSlider. I can't find any reference to a QVector in either of them.

This is my final step before I start banging my head on my desk.