Hello!
I have discovered that if you noodles connecting render layer Depth (z) and Vector (speed) to File Output node saved in 2.79, the noodles will be disconnected if you open them in a version before 2.79. Hopefully this does not mean other stuff is also broken.
Apologies if this has been noted elsewhere!
There is a change going on from Blender 2.78 to 2.79, so many more things are broken.
You can´t use files saved with 2.79 with earlier versions.
This is happening all the time with Blenderversions since the early days.
Personally I always keep the Blenderversion for the Blendfiles and I have a “InfoTXT” inside the file with things like the Version I created the file with and Addons that I used. If you want to reuse an Blendfile that is years old this saves you a lot of headaches.