If I understand correctly, you are trying to get a dotted quarter to display
as a dotted quarter, and not as a quarter an eighth tied together?

It seems to be dependant on which beat you are entering the dotted quarter note on.
If it is entered on the 1st or 3rd beat, it will display as a dotted note. But if
it is entered on the 2nd or 4th beat, you get two notes tied together.

I don't know of a way to control this, perhaps someone does.