Video clip not visible - Fusion Composition?

One of my video clips has be labeled with three stars in the lower right corner indicating a fusion composition. I don't know how this has happened and when the clip is played back it's all black. How do I make it normal?

I think I just found the solution myself. Right-clicking and selecting 'Reset Fusion Composition' seems to have deleted this issue. However I'm still interested in knowing what I've done to make it become a fusion composition in the first place.