At some point in the recent releases, it seems Jenkins can no longer runs background shell commands correctly. That is, it waits for the job to finish.

I have updated to the latest version of Jenkins and the SSH plugin. I have reproduced the problem with the following job:

echo 'Jenkins start:'
date
sh /tmp/test.sh &
echo 'Jenkins end:'
date

This produces the output:

+ echo 'Jenkins start:'
Jenkins start:
+ date
Mon Jul 21 14:20:40 EDT 2014
+ sh /tmp/test.sh
+ echo 'Jenkins end:'
Jenkins end:
+ date
Mon Jul 21 14:20:40 EDT 2014
Script end:
Mon Jul 21 14:20:50 EDT 2014

The script contains:

sleep 10
echo 'Script end:'
date

Considering this does not work over SSH shell script or a local shell script, my guess would be in the last few releases something changes with the escaping of an ampersand.