Problem with voices

[Sami Amiris]

I am sorry for any inconvenience to the group. I am a relative newbie, and I 
need help.

When I type this:

\version "2.14.2"

\score
        {
        \new PianoStaff
        <<
                \new Staff = "up"{
                \clef treble
                \new Voice = "upper"
                \autochange {
                \relative c''
                        {
                        \stemUp{        
                        \bar "|:" bes4 c bes' c \bar ":|" d1 \bar "|."
                        }}}}
                                
                \new Staff = "down"{
                \clef bass
                \new Voice = "lower"
                \autochange {
                \relative c'
                        {
                        \stemDown{      
                         bes4 c bes' c | d1 
                        }}}}
        >>
        }               

It doesn't split the voices, just puts them together into one. If the first 
relative is c' or less, all is well. To see how it should be, try it out like 
this:

\version "2.14.2"

\score
        {
        \new PianoStaff
        <<
                \new Staff = "up"{
                \clef treble
                \new Voice = "upper"
                \autochange {
                \relative c'
                        {
                        \stemUp{        
                        \bar "|:" bes4 c bes' c \bar ":|" d1 \bar "|."
                        }}}}
                                
                \new Staff = "down"{
                \clef bass
                \new Voice = "lower"
                \autochange {
                \relative c
                        {
                        \stemDown{      
                         bes4 c bes' c | d1 
                        }}}}
        >>
        }       

The only difference is the relative notes. This problem exists when the R.H. 
relative is greater or equal to c'' from what I have seen.      

What can I do?