As there was a bug in QWebKit regarding "unload" event. We have raised and also they have provided patch file to fix this issue. I have applied the patch in linux and compile the webkit and tested the attached patch with compiled webkit which is now working fine.
Below is the link for reference regarding unload issue. They have provided test webkit release for Mac in below URL but for other platform we need to apply the patch and compile the webkit until they provide webkit-releases for all platforms.