Thanks Guillem for pointing out this problem and even more for providing a fix! 
I just merged it.

(I extended the fix so that the translator raises an error on tasks with 
object fluents.)

I found a tiny bug in the translate module. When parsing the :functions block of 
a 
PDDL domain, the (typed) functions are incorrectly processed.
As far as I understand, this currently poses no problem, since only the total-
cost 
function is supported, but might provoke some headache in the future if FD 
starts 
supporting the object-fluents PDDL3.1 extension. The bug can be most easily seen 
by 
placing a breakpoint at pddl/tasks.py:146 - the variable the_functions contains 
some functions which are the result of incorrectly parsing the total-cost 
function 
type specifier "- number".
I'm attaching a patch with a possible workaround.