When sending a request as follows:

union smb_open io;	

	mem_ctx = talloc_init("raw_open");

	io.generic.level = RAW_OPEN_NTTRANS_CREATE;
	io.ntcreatex.in.flags = 0x16;
	io.ntcreatex.in.root_fid = 0;
	io.ntcreatex.in.access_mask = 0x196;
	io.ntcreatex.in.file_attr = 0;
	io.ntcreatex.in.alloc_size = 0;
	io.ntcreatex.in.share_access = 0;
	io.ntcreatex.in.open_disposition = 0;
	io.ntcreatex.in.create_options = 0x40;
	io.ntcreatex.in.impersonation = 0;
	io.ntcreatex.in.security_flags = 0;
	io.ntcreatex.in.fname = "bug.txt"; 
        io.ntcreatex.in.sec_desc = NULL;
        io.ntcreatex.in.ea_list = NULL;

	ret = smb_raw_open(c->tree, mem_ctx, &io);

Samba will return NT_STATUS_OK when in unicode mode.

But if SMBCLI_FORCE_ASCII is set in the environment, the samba server will
return NT_STATUS_FILE_IS_A_DIRECTORY.  

It goes without saying that there is no directory named bug.txt in the share.

This bug exists for all file names I have tested.