Grouping quavers and semiquavers in 4 4

I am new to writing out music so apologies if this an obvious question.

When I write out this bar, I separate the notes so that each beat starts on a new note, however, when I regroup the rhythms using the MuseScore tool it combines them so that the fourth beat begins partway through a note. This can be seen in the attachments, why is this?