I created a pull request that solves this problem: https://github.com/jenkinsci/pipeline-utility-steps-plugin/pull/56

Probably related to this issue: I had a "too many open files" error in linux, and the lsof command revealed thousands of open file descriptors resulting from Jenkins pipeline tee command.

Note that tee is executed in parallel tasks in my case.

A restart of the Jenkins service has temporarily solved the problem.

We just started using tee() in a workflow, and in less than 24h, one agent leaked enough descriptors to hit the per-process limit.  Use of tee() in this workflow was fundamental to the workflow itself, so this is a huge blocker for us (considering an agent restart is required to resolve).

jglick any update on https://github.com/jenkinsci/pipeline-utility-steps-plugin/pull/62 ? 

I am neither the author of the patch, nor the maintainer of the plugin.

There is a trivial workaround for some use cases: replace

tee('output.txt') {
  sh 'some command'
}

with

sh 'some command >output.txt 2>&1'

Of course this is not possible if you were redirecting output from multiple nested steps that could not be coalesced.

In our installation(2.176.4) tee on windows nodes works good with workflow-job plugin <=2.25. After upgrade workflow-job  plugin to 2.26+ version job with

node('windows')
{
tee {bat ... }
cleanWs()
}

drops with

ERROR: Cannot delete workspace: Unable to delete '...'. Tried 3 times...

Just running into this today. For I workaround i switched to use powershell as follows:

bat '''
   powershell "cmd /c '.\your.bat' | tee output.txt"
'''