Installer: shown progress is inconsistent

Binary package:
releases.qt-project.org/digia/2012-08-29/qt-windows-opensource-5.0.0-beta1-x86-offline.exe

Machine:
Windows 7 pro 64

It looks like the installation is pending at 29% progress since this state is shown for a while.

In "show details" view we can see that files from "Src" are being copied in background so there is actual progress made.

Progress jumps to 57% when files to "Desktop" folder are copied.

The progress bar is inconsistent with the actual progress of the installation