Strange Appearance of New Measure

I just started using MuseScore to transpose Kenny G's rendition of "Ave Maria" for the alto sax. I am using version 0.9.6.3 with Windows 7. Unfortunately, multiple incidences have happened where I am in the middle of typing notes in a measure that is the last on a line, when the measure will drop to the next line just as a new measure (of a whole note rest) will suddenly pop up before it - and by before it, I mean in between the treble clef and the key signature. Baffling, yes? Additionally, rests start appearing on top of the new notes I am typing. I unfortunately do not know any more details that keep leading to the incident; the only common thread is the typing on the last measure of a line. I have attached my file so you can see the problem for yourself. After being infuriated to the point of almost giving up on this program and getting out the old pencil and staff paper, I decided to give this one more shot by asking for help here. Could someone please tell me how to avoid this apparent bug?