Beware of updating to 8.5.2 (including FP1 and FP2) if you still need to replicate databases with a R5 server. Pushing data to the R5 server will not work as expected!
"In 852 a new flag UPDATE_2_MARK_READ_NEWNOTE is being passed on the call to NSFNoteReplicateExtended. This is caught and the "This function is not implemented on this version of the server" error is set. Working on a fix."
At least for 8.5.2FP1 (on linux) there's a hotfix available from IBM: 852FP1HF484