1. Default config is not working a expected

When just enabling the feature as described in docs:

The config part in job config.xml

  <orphanedItemStrategy class="com.cloudbees.hudson.plugins.folder.computed.DefaultOrphanedItemStrategy" plugin="cloudbees-folder@6.16">
    <pruneDeadBranches>true</pruneDeadBranches>
    <daysToKeep>-1</daysToKeep>
    <numToKeep>-1</numToKeep>
  </orphanedItemStrategy>

No pruning is happening ever and deleted branches are accumulated for ever.

2. Setting config options to 0 is showing errors

I tried to make things work and got some experimentations. Trying to set days to keep and max # of old items to keep to 0, UI produces errors of not a positive integer.

The config part in job config.xml:

  <orphanedItemStrategy class="com.cloudbees.hudson.plugins.folder.computed.DefaultOrphanedItemStrategy" plugin="cloudbees-folder@6.16">
    <pruneDeadBranches>true</pruneDeadBranches>
    <daysToKeep>0</daysToKeep>
    <numToKeep>0</numToKeep>
  </orphanedItemStrategy>

Saving this configuration make orphaned items to get deleted:

Evaluating orphaned items in XX » YY
Will not remove zz as XX » YY » zz #2 is marked to not be removed: This record is explicitly marked to be kept.
Will not remove zzz as XX » YY » zzz #71 is marked to not be removed: This record is explicitly marked to be kept.
Will not remove zzzz as XX » YY » zzzz #1 is marked to not be removed: This record is explicitly marked to be kept.
Will not remove zzzzz as XX » YY » zzzzz #28 is marked to not be removed: This record is explicitly marked to be kept.
Will remove z as it is #1 in the list