It looks to me like the fix for Killing processes started by builds on Unix was broken as of 1.553. (issue 22641) has broken the way how Jenkins scripts are executed on a Linux host
With version 1.575 when the shell script running the commands exits it now sends signal 15 which kills all child processes that have been started rendering our Linux test system unusable as sshd is being killed.
This was not the case in 1.574, which I had to revert to to get this working properly again.