Unfortunately bug fix 1190250 doesn't solve problem completely. This fix assumes that after FTPSetUser we always stay on MVS filesystem, but it's not true, it depends on STARTDIRECTORY server option (FTP.DATA).
When STARTDIRECTORY HFS in effect on the server, we stay on HFS filesystem, SYST returns "UNIX is operating system of this server. FTP Server is running on z/OS", servr_os set to "UNIX" and FTPDIR will use LIST -aL.
In my understanding, if z/OS FTP server reply "UNIX..." on SYST, it MUST also accept "LIST -aL", but it doesn't...
My proposed fix is: add
when temp~pos('Z/OS') > 0 then self~srvr_os = 'MVS'
after line 1835, to recognize z/OS FTP server as MVS anyway.