sometime lack string (QtEmbedded Qt4.5, linux)

[muny]

Hello.
When I display string by using QLabel, missing string sometime occur.
My environment is embedded(mips & Linux), and I use additional true type font.
I do not understand a cause.

QLabel* title1 = new QLabel(this);
title1->setText("ABCDE");
title1->setGeometry(100, 100, 100, 30);
title1->setFont(QFont("myFontFamilyName", 18));
 
QLabel* title2 = new QLabel(this);
title2->setText("VWXYZ");
title2->setGeometry(100, 200, 100, 30);
title2->setFont(QFont("myFontFamilyName", 18));

QLabel* title1 = new QLabel(this);
title1->setText("ABCDE");
title1->setGeometry(100, 100, 100, 30);
title1->setFont(QFont("myFontFamilyName", 18));

QLabel* title2 = new QLabel(this);
title2->setText("VWXYZ");
title2->setGeometry(100, 200, 100, 30);
title2->setFont(QFont("myFontFamilyName", 18));

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The code result have 4 cases.
case 1(about 10%):
BCDE on title1 label and WXYZ on title2 label.
case 2(about 30%):
ABCDE on title1 label and WXYZ on title2 label.
case 3(about 30%):
BCDE on title1 label and VWXYZ on title2 label.
case 4(about 30%):this is success case.
ABCDE on title1 label and VWXYZ on title2 label.

I hope that this code result always is case 4(success).
Do you know a cause of this problem?

Thanks.