Combining first and second voice in guitar score

Greetings, I'm relatively new to MuseScore and am trying to replicate an easy exercise for classical guitar, but can't combine a half note with dot in the second voice with eight notes in the first voice, even though this would seem like a simple notation - please see the original and a failed attempt using MuseScore. Combining quarter and eight notes as in example 3 (MuseScore 2) causes no problems, however. What am I doing wrong? Any feedback or help is greatly appreciated.
Luc