QPainter::drawText() slowdown

This is a simple benchmark, compiled to run both with Qt 5.2.1 and 5.3.0:

printf("\nwidth = %d, height = %d\n", w, h);
if (w > 800)
	w = 800;
if (h > 480)
	h = 480;
QPainter painter;
painter.setClipRect(0, 0, w, h, Qt::IntersectClip);
painter.setRenderHint(QPainter::Antialiasing);
painter.setRenderHint(QPainter::TextAntialiasing);

for (alphaOn = 0; alphaOn <= 1; alphaOn++) {
	painter.setOpacity(alphaOn ? 0.3 : 1.0);
	painter.setPen(Qt::black);
	startTest("2000x drawText", alphaOn);
	for (i = 0; i < TEST_REPETITION; i++) {
		int n = rand(64) + 1;
		str.clear();
		while (n--) {
			char c = rand(26 * 2);
			str += QChar((c >> 1) + ((c & 1) ? 'a' : 'A'));
		}
		painter.drawText(rand(w), rand(h), str);
	}
	endTest();

The whole program code needs to be cleaned and can be made available on request. startTest()/endTest() just do time capturing and storing the results.

Running with 5.2.1:

width = 720, height = 574
2000x drawText: 0.294s
2000x drawText mit Alpha-Blending: 0.415s
width = 800, height = 480
2000x drawText: 0.280s
2000x drawText mit Alpha-Blending: 0.439s

Results with 5.3.0:

width = 720, height = 574
2000x drawText: 0.341s
2000x drawText mit Alpha-Blending: 0.555s
width = 800, height = 480
2000x drawText: 0.339s
2000x drawText mit Alpha-Blending: 0.602s

Repeating the runs gives jitter of drawText+Alpha test in the range of 10ms, so the effect is actually there. All tests were run using linuxfb, but using minimal does not give any difference. In fact I originally observed this on a even slower ARM machine where the results look like this:

2000x drawText: 4.919s
2000x drawText mit Alpha-Blending: 4.617s
2000x drawText: 23.891s
2000x drawText mit Alpha-Blending: 6.275s

For reference: a similar test on this machine using Qt 4.8:

Text Solid 4,663
Text Alpha 4,619

Since I can't guarantee the same build environment is used for 5.2 and 5.3 on the slower device I repeated the test on the BBxM.