I would also like to report this issue for Windows Server 2008R2.

I did happen to find a work around:

1. Open config.xml for the particular job you want
2. After the label element add one of the following
   • <whenToLabel>success</whenToLabel>
   • <whenToLabel>always</whenToLabel>
3. So it should look something like this
   • <hudson.plugins.tfs.TFSLabeler plugin="tfs@3.1.1">
     <labelName>MyLabel-123<labelName>
     <whenToLabel>success</whenToLabel>
     </hudson.plugins.tfs.TFSLabeler>
4. Restart Jenkins Server
5. If you have to make changes to the job
   • Manually update xml file, or
   • Run through steps 1 through 4, after you makes changes through UI

I know these steps are not ideal, but at least you can label without writing a separate script or Job.

I submitted a pull request that seems to have fixed to issue.

https://github.com/jenkinsci/tfs-plugin/pull/29

I also observed that whenToLabel is not saved to the job's config.xml.
Although, adding it manually did not fix it in my case (might be another configuration problem on my side).

Hannes, you need to reload configuration after adding it manually.

It seems no one is maintaining the repo anymore. I'll try to gain access so I can merge my pull request that fixes this issue.

Thanks for pointing that out. It seems to work after reloading the configuration from disk.

Code changed in jenkins
User: Chad Strauch
Path:
src/main/java/hudson/plugins/tfs/TFSLabeler.java
http://jenkins-ci.org/commit/tfs-plugin/98af3db1a544d9e43512add0be0ccd5bdf3e6631
Log:
https://issues.jenkins-ci.org/browse/JENKINS-23344 - Fixed whenToLabel in config.xml

The overridden newInstance() method was causing the <whenToLabel>
element to be removed from a job's config.xml file. TFSLabeler is
already instantiated because of @DataBoundConstructor.

Code changed in jenkins
User: Olivier "Oli" Dagenais
Path:
src/main/java/hudson/plugins/tfs/TFSLabeler.java
http://jenkins-ci.org/commit/tfs-plugin/37e4c3b763ec0b4c94290abdeaab6b9a597b3d8b
Log:
Merge pull request #29 from boatski/JENKINS-23344

JENKINS-23344: Fix missing whenToLabel in config.xml

Compare: https://github.com/jenkinsci/tfs-plugin/compare/6651056f252b...37e4c3b763ec

Fixed in version 3.2.0