When checked, one would think that the keepass install directory would be used. Testing however shows that actually keepasssync uses the directory where its plugin dll is located - and keepass relocates its plugins to per-user 'PluginCache' subdirectories - making the result very confusing.
Anonymous
A temporary workaround is to copy
PLINK.EXEandPSCP.EXEfromProgram Files\KeePassto%USERPROFILE%\AppData\Local\KeePass\PluginCache\*\(KeePassSync.dll should already be there).