QFileDialog - No overwrite confirmation when used with setDefaultSuffix() (GTK)

This issue is present when a native QFileDialog is in QFileDialog::AcceptSave mode and is set to use a default suffix (example below).

QFileDialog fileDialog;
fileDialog.setFileMode(QFileDialog::AnyFile);
fileDialog.setAcceptMode(QFileDialog::AcceptSave);
fileDialog.setDefaultSuffix("txt");
fileDialog.setNameFilter("Text (*.txt)");

The problem is when the following sequence occurs:

1. The user navigates to a folder where a file "text.txt" exists.
2. The user enters "text" into the textbox (without the ".txt" suffix).
3. The user presses return or clicks "save".
4. The dialog returns "text.txt" without requesting overwrite confirmation from the user.

This issue seems to be present in Linux. I have tested it using Windows and OSX and the confirmation is requested.