Hello,
I tested the behaviour today and it behaved like the description from @mykalrudie .
Based on the Keywort _CYCLIC we can asume that @christoph.hilchenbac did his Test in the Automation Studio ST-Code and not in an Motion ST-Code. Motion ST-Code has the Keyword _MAIN for the Code-Section.
Source of AS-Help about RETRUN in ST-Motion
I will create a Support-Request about this topic, and try to give updates here.
If you want to keep updated on this topic, you should create your own Support-Ticket via local Support.
Greetings
Michael Bertsch