Accidental not properly notated in score

[Patrick Karl]

Can anyone explain why the 2nd d-sharp is not notated in the music in  
the following snippet:

\version "2.12.2"

\relative g'' {
        \partial 4 r4
        r2. dis4
        e2.

        \repeat volta 2 {
                \partial 4 c8 dis
                e2.
        }
}

I understand that I could get it notated properly by writing it as  
"dis!", but that would require that I notice the need.

Thanks.