Sum does not seem to simplify before using subs

[nicoguaro]

I have an expression of the form

fun = Sum(x**(k + 4)/(k*x), (k, 0, oo))

and, when I try to substitute x for 0 I get

Sum(0**(k + 4)*zoo/k, (k, 0, oo))

I try using simplify before

simplify(fun).subs(x, 0)

I obtain the same

Sum(0**(k + 4)*zoo/k, (k, 0, oo))

But If I use expand

expand(fun).subs(x, 0)

I get

Sum(0, (k, 0, oo))

I just checked with the ratio of two polynomials

 (x**2/x).subs(x, 0)

and it returns 0. Is this a bug or is the expected behavior for summations?

[oscarbenjamin]

Some examples are working now

In [118]: simplify(fun).subs(x, 0) 
     ...:                                                                                                                                                     
Out[118]: 0

In [119]: expand(fun).subs(x, 0)                                                                                                                              
Out[119]: 
  ∞    
 ___   
 ╲     
  ╲   0
  ╱    
 ╱     
 ‾‾‾   
k = 0  

In [120]: _.doit()                                                                                                                                            
Out[120]: 0

This one still doesn't work:

In [117]: fun.subs(x, 0)                                                                                                                                      
Out[117]: 
  ∞             
 ____           
 ╲              
  ╲    k + 4    
   ╲  0     ⋅zoo
   ╱  ──────────
  ╱       k     
 ╱              
 ‾‾‾‾           
k = 0