I have a project in which I've defined svn:externals:

...
src/main/webapp/VUM -r37781 svn://svn/VISIONA/CSS/trunk/app/src/main/webapp/VUM
src/main/java/visiona/vum -r37781 svn://svn/VISIONA/CSS/trunk/app/src/main/java/visiona/vum
...

After a build of this configuration I see correct logs in console output:

...
Fetching 'svn://svn/VISIONA/CSS/trunk/app/src/main/webapp/VUM' at 37,781 into '/var/lib/hudson/jobs/CSSKB2/workspace/app/src/main/webapp/VUM'
...
Fetching 'svn://svn/VISIONA/CSS/trunk/app/src/main/java/visiona/vum' at 37,781 into '/var/lib/hudson/jobs/CSSKB2/workspace/app/src/main/java/visiona/vum'
...

But 'revisions' section states:

svn://svn/VISIONA/CSS/trunk/app/src/main/webapp/VUM : 36018
...
svn://svn/VISIONA/CSS/trunk/app/src/main/java/visiona/vum : 37118

The external's version was once 36018 but is 37118 now.