QDateTime becomes "<unavailable>" when setting QTimeZone

1. Stop at a breakpoint in the last line of the following code:

       QDateTime x = QDateTime::currentDateTime();
       QTimeZone tz("UTC+05:00");
       x.setTimeZone(tz);
   

   This is a simplified version of testLongEvaluation1() in simple.pro.
   Both x and tz are displayed correctly in Locals and Expressions view.

2. Step forward.
   x becomes "<unavailable>".

Creator should still display a value for x after setting the timezone.