multistaff use of rhythm mark snippet

[Qian Li]

I'm using one of the rhythm marks from the lsr for a multistaff piece. I only want the rhythm mark to show up on one of the staves in transition from a polymetric part back to same meter with the other staves, but the marking always prints over the top staff. 

I've attached the files; document.ly is the one to run. The problem is at m. 55, line 430 in content.ly. (Please ignore the metric misalignment after m 55.) 

What is the context that puts it on the top staff and how do I modify it to show on the second staff only?

Many thanks.

Qian Li

document.ly
Description: Binary data

content.ly
Description: Binary data