I've seen a handful of people mention this. I'm not sure if it's a bug but it's strange behavior. Many people describe not being able to recreate it but I figured out how to recreate it. I'm just not sure what's causing it. Moodle 2.6 didn't demonstrate this behavior; I'm not sure about 2.7.

To make it disappear
1. Create a Wiki page (collaborative wiki)
2. Click on Files & upload a file (any kind)
3. Save
4. Navigate to Edit & type any amount of text
5. Save
6. Navigate back to files and discover your file is no longer there.

To make it stay
1. Create a Wiki page (collaborative wiki)
2. Navigate to Edit & type any amount of text
3. Save
4. Click on Files & upload a file (any kind)
5. Save
6. Navigate back to files and discover your file is still there.

Can anyone shed light on this?