I posted a similar issue, My default font is times and works perfect if its a 1.5.3 NEW document, when I use an 1.5.2 or earlier document in 1.5.3, if I highlight text right to left it mostly stays default, if I go left to right I get Ariel
I have fixed by using styles or highlighting correctly (long as I don't go past last character it works) Style began to crash on me so I stopped that for now, I also found highlighting and starting ti type in desired font name make fixing easy