First of all, I can reproduce this in Syncthing 1.7.0. Please forgive me in case the problem has been fixed since then.
Steps to reproduce:
- Create a new folder on Device A, set it to “Send Only”, and add some files to it.
- Share the folder with Device B.
- Accept the folder on Device B and set its type to “Receive Only”.
- Delete some files from the folder on Device B. The folder is now marked “Local Additions”.
- Change the folder type on Device B to “Send & Receive”.
- Both folders show “Up to Date”, but the files remain deleted, which is reflected in the “Local State” on Device B.