QImage and QImageReader refuse to load any valid JPEGs in release build

[Violet Giraffe]

Greetings.

The problem is as described in a title: QImageReader.canRead() and QImage.load() return false when my test app (Windows platform) is linked with release QtCore and QtGui dlls, while it works fine in debug. BMP files are loaded OK in any configuration,
I've tried 3 versions of QtCore and QtGui dlls: the ones from official installer (compiled with MSVC2008, x86), compiled with MSVC2010 x64, and compiled with ICC x64.
I have also tried giving my app with the official 2008 x86 dlls to my friend, he reported the same problem. We both use Windows 7, if that even matters. Qt version is 4.7.3.

Any ideas are appreciated. Thanks in advance.