Recently I converted my GWT web-app (GWT 2.4.0) to a maven project. I am using maven 2.2.1, gwt-maven plugin (2.4.0), Eclipse Indigo (3.7) and the m2ecl
The reason for the Maven build is more than likely an enabled Maven Project Builder (Project properties > Builders).
You can disable it and -- as long as you have the Java Builder selected -- Eclipse will continue to compile edited files.