Can't attach platform sources

Sometimes I want to be able to see the platform sources easily...

But 'Attaching sources' doesn't seem to work. 

I tried doing this with org.openide.util.actions.CallableSystemAction, but I get the same result with other classes as well.

Tried doing "Attach Sources.." and selecting the downloadable zip with platform sources, used the zip called netbeans-8.1-201510222201-platform-src.zip

Tried checking out the hg-repo, and added the whole 'main' folder.

Tried using the specific folder that file is in, main\openide.util.ui\src\org\openide\util\actions.

Tried the 'download' option

Neither worked, and I don't get any sources. 

I checked in \AppData\Roaming\NetBeans\8.1\var\log to see if there was any useful log messages, but couldn't find anything related. 

Any ideas? 

This is on windows 7, netbeans 8.1.