@VRonin
After some headache days I found the problem. The FilterWindow widget had set wrong the parent in children widgets, so, the right way would be :
void FilterWindow::setUi(std::string tittle)
{
Frame = new QFrame(this); //Here it must be this, to set the widget itself as the parent
Frame->setObjectName(QStringLiteral("Frame"));
Frame->setFixedWidth(281);
Frame->setFixedHeight(89);
Frame->setStyleSheet(QLatin1String("QFrame\n"
"{\n"
" border-style: solid;\n"
" border-width: 0px;\n"
" border-radius: 4px;\n"
" border-color: transparent;\n"
"}"));
Frame->setFrameShape(QFrame::StyledPanel);
Frame->setFrameShadow(QFrame::Raised);
Frame->setAttribute(Qt::WA_DeleteOnClose);
checkBox = new QCheckBox(Frame);
checkBox->setText(tittle.c_str());
checkBox->setObjectName(QStringLiteral("checkBox"));
checkBox->setGeometry(QRect(0, 0, 248, 35));
checkBox->setAutoFillBackground(false);
checkBox->setStyleSheet(QLatin1String("QCheckBox\n"
"{\n"
" background-color: rgb(128,139,143);\n"
" color: white;\n"
" border-radius: 4px;\n"
" padding-left: 8px;\n"
"}\n"
"\n"
"QCheckBox::indicator:unchecked {\n"
" image: url(:/OptiNanoPro/uchk);\n"
"}\n"
"\n"
"\n"
"QCheckBox::indicator:checked {\n"
" image: url(:/OptiNanoPro/chk);\n"
"}\n"
""));
checkBox->setChecked(true);
ArrowBtn = new QPushButton(Frame);
ArrowBtn->setObjectName(QStringLiteral("ArrowBtn"));
ArrowBtn->setGeometry(QRect(246, 0, 36, 35));
ArrowBtn->setAutoFillBackground(true);
QIcon icon;
icon.addFile(QStringLiteral(":/OptiNanoPro/DownArrwLd"), QSize(), QIcon::Normal, QIcon::Off);
ArrowBtn->setIcon(icon);
ArrowBtn->setIconSize(QSize(36, 35));
ArrowBtn->setFlat(true);
Table = new QTableWidget(Frame);
Table->setObjectName(QStringLiteral("Table"));
Table->setGeometry(QRect(0, 35, 281, 31));
Table->setStyleSheet(QLatin1String("QTableWidget\n"
"{\n"
" background-color: white;\n"
" border-radius: 0px;\n"
"}"
"\n"
"QCheckBox\n"
"{\n"
" color: white;\n"
" padding-left: 8px;\n"
"}\n"
"\n"
"QCheckBox::indicator:unchecked {\n"
" image: url(:/OptiNanoPro/uchk);\n"
"}\n"
"\n"
"QCheckBox::indicator:checked {\n"
" image: url(:/OptiNanoPro/chk);\n"
"}\n"
""));
ResetBtn = new QPushButton(Frame);
ResetBtn->setText("Reset");
ResetBtn->setObjectName(QStringLiteral("ResetBtn"));
ResetBtn->setGeometry(QRect(0, 66, 169, 23));
ResetBtn->setStyleSheet(QLatin1String("QPushButton\n"
"{\n"
" background-color: white;\n"
" border-width: 1px;\n"
" border-style: solid;\n"
" border-color: rgb(86,86,84);\n"
" border-radius: 3px;\n"
" color: rgb(86,86,84);\n"
"}"));
AplyBtn = new QPushButton(Frame);
AplyBtn->setText("Apply");
AplyBtn->setObjectName(QStringLiteral("AplyBtn"));
AplyBtn->setGeometry(QRect(169, 66, 111, 23));
AplyBtn->setStyleSheet(QLatin1String("QPushButton\n"
"{\n"
" background-color: white;\n"
" border-width: 1px;\n"
" border-style: solid;\n"
" border-color: rgb(86,86,84);\n"
" border-radius: 3px;\n"
" color: rgb(86,86,84);\n"
"}"));
}