Unrecognized option: -S
-S option: Does nothing in ManaPlus (works only in ManaVerse). Crashes in Mana, however, which isn't good.
It's formally documented as:
-S --uniqueSession : Disables back to login (Launcher/Vault/Steam only option!)
(In other words, an instruction to close the client when quitting, rather than showing server list).
Feature itself might be low priority, but you might not want to crash.
PS. It technically also removes the "Switch server" button from ESC.