Change order of above staff objects

[Helge Kruse]

Hello,

I have a score with some long tempo items. Since my part has multiple 
full bar rests I get several rehearsal marks in the area of the tempo. 
Unfortunately they are placed above the tempo. How can I get the 
rehearsal mark immediately above the staff line?

Minimum example:

\version "2.18.0"
{
  \tempo "Allegretto ma non troppo" 4=100
  \time 4/4
  %\compressFullBarRests
  R1*2 \mark\default
  R1 R
<b' d'' f'' a'' %c'''
>
}

The rehearsal mark is too high. Somehow it gets a lower place when I 
remove *both* comment characters.

Regards
Helge