Font Changes in Apple Works

You have two separate topics going. One at a time here:

So with a new document open, you've gone to Appleworks > Preferences > General > Text, and set the font and the size, and clicked on the "Make Default" button, right? If that doesn't work, try removing the file "com.apple.appleworks.plist" located in: [user]/Library/Preferences, and/or reinstall AppleWorks.

If you're working in a document with more than one font, and you point and click on a specific area of text with a font other than the one you're working in currently, then the following characters you type from that specific area will be displayed in the new font. Also, if you cut and paste text in a font different than the one you are working in currently, and you start typing up text again, the following characters you type from there on will be in the format of the last character of the text from the cut and paste. To change it back, select the font you worked with just before the fonts switched on you from the font menu.