I blocked off a lavafall, and when I came back in the same chunk after a short trip, I saw some flowing lava flowing from nowhere!

Steps to Reproduce:

1. Find a naturaly generated lavafall (not above lava lakes)
2. Try to block the sorce off
3. repeat some times the 2 steps above 

Observed Results:
The lava sorce will stop being connected with the flowing part, but that part can still exist there. Even after updating it, it will not go away.

Expected Results:
The flowing lava should drain after being updated

Screenshots/Videos attached: Yes