> Well, the thing is that i pass two (apparent) identical values into the same function,

Even if they have the same *numeric* value, they aren't the same kind of 
value, and they aren't the same function.

One is <type 'numpy.float64'> and the other is <class 'float'>. When you 
call ** (exponentiation), that calls two different methods. One raises 
a warning and returns NAN, the other converts to complex.

This has nothing to do with linspace. See my simplifed example code 
which doesn't use it.