Im using latest shotcut version on 64 bit Windows 7 machine in Multimedia classes. Few students had problems when exporting. They just have to add logo over some slideshow and export video. Their video behaved strange. I discovered that they exported to the file from which they load the source video and choose that they want to replace the original file. This is quite common problem. I guess some people reporting render problems did it at the same fashion.
Maybe it will be good to not allow user to replace original file, or to make some backup copy or whatever in some future version.