I see from Jakob's email that the bug can be reproduced on CIFS without 
EncFS.  However, there's still something wrong here, as Emacs has code 
to work around the CIFS bug; see the comment about CIFS in 
emacs/src/fileio.c starting at line 4897, here:

http://git.savannah.gnu.org/cgit/emacs.git/tree/src/fileio.c?id=a56eab8259568ea1389e972623e46359e73c0233#n4897

Unfortunately, this workaround for the CIFS bug does not appear to 
suffice for EncFS over CIFS.

Bertrand, can you please try the attached program, both on plain CIFS 
and on EncFS over CIFS?  It attempts to mimic Emacs's actions more 
precisely than the previous test program, which may help us to narrow 
down the problem.  Thanks.