Thunderbird composition - Paragraph format/body text - solved

Thunderbird keeps changing my email composition from body text to Paragraph format. It doesn't matter how many times I go Tools>Options>Composition>General and then uncheck "Use Paragraph format instead of Body Text by default" every time I relaunch Thunderbird that box has rechecked itself. It's a minor annoyance, but I can't find a way to stop this setting from defaulting back to Paragraph format. All I want is to be able to compose an email in Body text without having to change this setting every time I launch Thunderbird. Any advice??