I noticed that the line spacing defaults to "Normal" which is 0.5 spacing,
whereas I have to select "No Spacing" to get single spacing. I don't know why
it defaults to that. I am not aware that I set it.
Press Ctrl+Alt+Shift+S to display the Styles task pane. Click the Manage
Styles button. On the Set Defaults tab, change the line spacing to "Single."
Check the "New documents based on this template" option, and then click OK.