I'm using FreeFileSync version 5.8. I use lastpass addon for firefox on Ubuntu 12.04 x64. It has a file of lastpassffplugin which causes FreeFileSync to freeze when it tries to copy it over (even though firefox is closed). In nautilus's properties dialog, it lists file type is pipe (inode/fifo) and it is a zero byte file. The location is /home/user/.lastpass/pipes. I am not sure why the freeze occurs. For now, I have just excluded the pipes folder via filter.
The file freezes FreeFileSync on both my desktop and my laptop.