I know this has been discussed some during the debugging of 11.28, but it still seems to be an issue.
The clef change at the end of a measure affects both staves in the PianoStaff (not sure what happen in other Staffs). So one staff with lots of notes gets lots of whitespace where the clef appears in the other staff.
This seems rather like a bug, I suppose. I would point out that, while ver. 2.10.x handles it better, it still displays the problem.
My question is if there is some way to override the space a clef occupies in the staff, without resorting to strict note spacing (which affects all kinds of stuff)... and if there is hope of completely eliminating this behavior at some point ;^)