Petrof mute bar

[J Patrick Draine]

Petrof experts,
A customer has called complaining that her recently purchased Petrof 
upright's practice (middle) pedal mute bar is not engaging. I don't 
recall the exact setup on the Petrof, but do remember thinking it was a 
bit odd (ie not exactly the same as more familiar Yamahas or older 
American uprights).
Any helpful hints as to why this one has disengaged, and how best to 
prevent it in the future?
TIA,
Patrick Draine