I seem to have stumbled across a small bug with my new D7100, I don't know if its exclusive to my copy only or if it affects all cameras.
Exclusive to video mode, when the shutter speed is set to high, and with a combination of having a higher iso, I noticed a small black/glowing blob on the bottom left of the screen.
The lens is brand new itself, and the issue is the same regardless of which lens I use, sensor is visually clean as well.
It's more pronounced with a higher shutter speed and higher ISO so it shouldn't be a problem for shooting under normal conditions. On slower shutter speeds (like 400 and under) you won't really see it, its similar to the field of depth going smaller and going out of focus.
If you hit the right settings and it affects your camera you'll see what I mean, anyone else have this?