Ran across it and did some testing on the spot to recreate it, managed to have it happen 6 times.
Have a flashlight turned on, and fly around looking at another astronaut, they will sometimes vanish leaving the nav marker visible.
Showing bug
http://i.imgur.com/Y2nhhSC.png
After moving camera a bit.
http://i.imgur.com/v2yM7Ed.png