Key and time signatures duplicated in first measure

I have MuseScore 1.3 revision 5702 on Ubuntu Linux. I'm following the tutorial, but have ended up with two time signatures and two key signatures in the first measure of all voices. There doesn't seem to be a way to get it back down to only one key and time signature. When I enter notes in the 1st measure of the 4th voice, the notes appear between the two signatures. I can select the first key and time signature and delete them, but notes entered in the 1st measure appear before the (former) 2nd key and time signature, instead of after them.