I'm actyally having the same issue!
Are you using yocto rocko with an imx6 module? I've see that if you're trying to load local html pages in the qtwebengine .. it's working. I suppose is due to the version of chromium on which qtwebengine is based.
I finally got to solve this by myself. I only had to add 'libqgfxtransformed.so' to my target's /usr/lib/qtopia/plugins/gfxdrivers folder. I then ran my app using the '-qws -display transformed:rot90' switch and I got my rotation done!
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