Release Strategy is not set / Reset if previous version is active
SAP Materials Management
Release strategy will not be effected if Version management is not complete.
Version management on the purchasing documents are closely related to release strategy and vice versa. if pervious version is not completed , any change in the document will be effect the release strategy. This is a standard system functionality.
Version is a collection of all the changes performed on the document and will be active only when completed. Release strategy is programmatically set to trigger only when version is completed.
Reference
Basic understanding of Version Management