Writing to a samba share from Yosemite - v. weird
I'm not sure because i knever used the option, but maybe you can try "unix extensions = yes" ( Darwin is BSD )

I also suggest to use as less params as possible, it's easyer to find what went wrong that way. These are mine and it works.


   [sharename]
   comment = My Shared Volume
   browsable = yes
   read only = no
   writable = yes
   path = /home/dimitri
   guest ok = no
   create mask = 0750
   directory mask = 0755
   oplocks = no


keep it simple if you want to avoid a comples headache