In qtableview.cpp at the end of QTableView::paintEvent() a first horizontal (vertical) grid line is drawn when the horizontal (vertical) header is hidden and the scroll mode is "ScrollPerItem". The problem is that this is drawn over the first row (column).

The results are (see picture):

• When the horizontal header is hidden, the first row height is one pixel shorter than the other rows height.
• When the vertical header is hidden, the first column width is one pixel shorter than the other columns width.

Small test case:

#include <QtGui>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QMainWindow w;
    QTableWidget table(200,3);
    table.horizontalHeader()->setVisible(false);
    table.verticalHeader()->setVisible(false);
    w.setCentralWidget(&table);
    w.show();
    return a.exec();
}