Taskbar entry is displayed for the QDialogs with a parent that doesn't have a taskbar entry in GTK 3

As the documentation says, the QDialog got to share it's parent's taskbar entry, so if the QDialog grandparent is created, it got to share it's parent's taskbar entry, which in case is the grandparent's one. This is what happens on Windows, but on GTK 3 the taskbar entry isn't shared between the child and the grandchild, so the grandchild has it's own entry displayed.

Example:

QDialog *d1 = new QDialog();
d1->setWindowTitle("d1");
QDialog *d2 = new QDialog(d1);
d2->setWindowTitle("d2");
QDialog *d3 = new QDialog(d2);
d3->setWindowTitle("d3");
QDialog *d4 = new QDialog(d3);
d4->setWindowTitle("d4");

d1->show();
d2->show();
d3->show();
d4->show();

Expected behaviour: Only d1 has a taskbar entry as it has no parent.

Actual behavior: d1, d3 and d4 have a taskbar entry, d2 - hasn't one.