Why each element of the var_importance have the same value ? letter_recog.cpp opencv3.0 gold

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Getting output after compiling letter-recognition.cpp of sample code:

The database ./letter-recognition.data is loaded.

Training the classifier ..

Recognition rate: train = 86.2%, test = 82.0%

Number of trees: 100

var# importance (in %):

0 6.3

1 6.3

2 6.3

3 6.3

4 6.3

5 6.3

6 6.3

....

`model->setCalculateVarImportance(true);

Mat var_importance = model->getVarImportance(); `