programming error with \markup \vspace used in \header

[Thomas Morley]

Hi,

the following code returns:
  programming error: Improbable offset for stencil: -inf staff space
  Setting to zero.
although the printed output seems to be correct.

\version "2.19.1"

\header { title = \markup \vspace #10 }

\markup "xy"


I noticed the error with 2.17.97, 2.18.0 and 2.19.1
2.16.2 returned no error.
A stand alone \markup \vspace #10 throws no error.


Cheers,
  Harm