\mark and slur

[Gianmaria Lari]

This compiles well

\version "2.19.65"

\fixed c' {

  c4 c c d 

  (c4) c c c 

}

but when I add a \mark like this

\version "2.19.65"

\fixed c' {

  c4 c c d 

  \mark "X" (c4) c c c 

}

it doesn't. I know the problem is related to the slur and I can move the mark before d but why I should not be able to put it at beginning of the second measure?

Thank you, g.