What if you temporarily remove the release path configuration for document type KR? Can you then post the documents with the transaction? (Just to make it sure that the problem is not somewhere else.) I think the transactions were OBWA, OBWD, etc.
What if you check field VBKPF-XWFFR for some of the document that should not require the release (=posting should be possible directly)? If I remember correctly, there will be value X, if the document requires the release. Then you will know if there is something wrong in your configurations.
Also make sure that it is not an authorization issue.
Try also to search OSS notes. I think there have been some issues with this functionality in the past.
Regards,
Karri