Make sure you are on the latest 'core' and 'jbosstools-forge', also rebuild the 'gradle' addon locally from sources:

2:32 run the eclipse UI
2:32 then install the gradle addon
2:32 then try new-project
2:32 change project type to Java Library
2:32 change build system to Gradle
2:32 change Project type to Forge Addon
2:32 build system remains "Gradle"
2:33 this is incorrect - i verified that NewProjectWizard is doing the right thing in a test. so I think eclipse must be doing something wrong.
2:33 Now, If you try to set the build system to maven, then back to gradle, the eclipse UI hangs completely
2:33 it loops constantly trying to get the default values for some reason.