It may or may not be related, but libsmbclient seems to have (had) some peculiarities regarding the smb.conf file, as commented on in the module:

  # Actually libsmbclient will segfault if it can't find file
  # $ENV{HOME}/.smb/smb.conf so I will test if it exist,
  # and create it if no file is found. A empty file is enough ...
  ... creation of an empty $ENV{HOME}/.smb/smb.conf
[download]

So maybe libsmbclient does not crash nowadays but doesn't necessarily respect /etc/smb.conf if it doesn't find a local file.