Since enabling maven nature and build MyEclipse is creating duplicate test class files in target-eclipse/test-classes in addition to the target/test-classes folders I specified in the java build path source tab.
What happened was, I took an existing project, and enabled it for maven by editing the .project file ( since there is no way to do that otherwise … another feature request )
At some point after that, target-eclipse started showing up. Later I found that my build path settings had been changed, so that the default output folder was target-eclipse. I changed it back to target and so far it is still set for that.