Eighth note's flag crosses notehead when stem is directed down
Steps to reproduce:
1) Add an eighth note somewhere in the bottom part of the staff (G pitch in this example).
2) Move it to the second voice.
Result: flag intersects a notehead
For a comparison see how the same situation was handled by MuseScore 2:
OS: Debian GNU/Linux 9 (stretch), Arch.: x86_64, MuseScore version (64-bit): 3.0.0, revision: 77b832b