OK, after further investigation this is definitely an issue with the commons-net FTPClient.listFiles method which is called from the FTPFile list(String path) method in SI's FtpSession class. Although I'm not able to reproduce locally it seems the directory listing parser fails (for certain ftp servers?). For the same server in question in my case, if I first change the working directory then call listFiles(".") I get the correct list of files back. I'm attaching another test which illustrates this. There's also evidence that spaces have been a pain point for commons-net in the past:
Given all of this, is there an easy way to swap FTP clients or override the FtpSession.list method in SI?