I am using version 12.0.6 on Vista and every time I start routing a new track I get an arc instead of a 45 degree mitre. I can't find anything in the help files about how to change this setting. It's easy to fix the tracks afterwards but annoying to have to do it.
There are 3 different default settings under [Settings], [Preferences] for this, on the Schematic Interaction, PCB Interaction and PCB Tracks tabs. You want the one on PCB Tracks.
Also, when you're laying tracks, the hot key <M> will cycle through all possible options for this, including flipped versions.
The setup isn't saved in the Technology file - it's saved with the program so it applies to all designs