OS: Windows 7
Graphics card: ATI Radeon HD 5700 Series
Blender version: 2.78 Release Candidate 1 - Hash: 0e5089c
In compositor, I have an Image Node, with a Multilayer EXR image opened and connected Output points to other nodes.
Sometimes when I open another image in the same node, all noodles get disconnected, sometimes they don't.
All images same using Multilayer EXR with the same settings and same passes.
I noticed that the noodles get disconnected when I open an image that is saved using the (Animation) button, while when I open images that were saved using (Render) button, and (F3) to save, the noodles keep connected.
Please refer to the following link on BSE, where I uploaded 2 animated GIF files that show both cases: