Jenkins multibranch pipeline won't prune deleted branches
Finally I found the hidded switch by myself. Feeling little bit stupid, though.
In the job configuration you can specify for how long to keep old items. When setting up this job initially I must have mixed up this setting with the setting which tells jenkins for how long to keep old builds. So it was set to 30 days.
Btw.: The number of builds kept for the individual branches are not affected by this setting...:
Orphaned Item Strategy (how it looked like)
Orphaned Item Strategy (how it should have looked like)
However to immeditaly get rid of orphaned branches one must not enter a number there, like:
