I\'ve downloaded the source for all the Maven JARs in my buildpath using Maven->Download Sources and mvn eclipse:eclipse -DdownloadSources=true, which worked! W
mvn eclipse:eclipse -DdownloadSources=true
I think I fixed this for myself by updating my Eclipse m2e. I think I had version ~1.2, and then updated to latest [as of writing] 1.6.2.
The Eclipse Bug comments helped me figure this out.
Now I can debug into my gquery-dnd-bundle-1.0.6!