Operating system: Windows-10-10.0.17134 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 419.17
Broken: version: 2.80 (sub 71), branch: blender2.7, commit date: 2019-05-22 21:50, hash: rBa1ad71304c2d
Short description of error
Knife tool often creates double geometry in cut areas. Sometimes doesn't even finish the cut properly. When you zoom in during cutting and move cursor out of the model it moves the cut point to 0,0,0 location.
Exact steps for others to reproduce the error
I think everything is in the video.