Clearing the undo stack of a QTextDocument triggers critical exception

When i call QTextDocument::clearUndoRedoStacks(QTextDocument::UndoStack) an index out of bounds exception is triggered by QVector. This i originates from the QTextDocumentPrivate class, in fact in qtextdocument_p.cpp line 1105, there is the following code snippet:

for (int i = 0; i < undoState; ++i) {
            QTextUndoCommand c = undoStack.at(undoState);
            if (c.command & QTextUndoCommand::Custom)
                delete c.custom;
        }

which seems an obvious mistake. This code is executed only when passing QTextDocument::UndoStack as argument, not with RedoStack or UndoAndRedoStacks.

Here is the code to replicate the exception

QTextDocument doc;
QTextCursor c(&doc);
c.insertText("lorem ipsum");
doc.clearUndoRedoStacks(QTextDocument::UndoStack);