SYST command is only used when connecting to some FTP servers as part of server brand detection. It is not currently possible to bypass this, and although it is not absolutely necessary for this call to be made, it was never reported to cause any issues because even if the FTP server rejects the command, our code should simply ignore that and continue without any problems. In short - it should not err out. If it does, something is wrong somewhere. Does your client's FTP server close the connection when it receives the SYST command or something like that?
Anyway, we can easily add an option to disable this altogether. This should solve the problem regardless its cause. I will send you a link to a current build with this option soon.
The fix was published as a part of Release 2012 R1.
DoNotDetectFeatures option now turns off server feature detection completely, not only the one using the FEAT command.