After commit of a file, brought in with svn:externals property, subsequent update of the containing directory returns "svn: warning: W155035: The specified path has an unexpected status". scn:externals for this file has neither peg to operative revision set, and is relative to current directory. However, file is restored in process with message "Restored 'somefile.ext'" - seemingly from 'pristine'. Fresh checkout of the directory works properly. Also, temporary removing the property (or changing local name), updating, and changing it back, fixes the issue too.
Original issue reported by cavaler