Hi, I've tried your method on either staff but it doesn't solve the problem.
I've figured out a great workaround though. Just insert a key signature for
the second staff which is the same as the first staff, and then use
\override Staff.KeySignature #'transparent = ##t to make it invisible. By
using that the rests are aligned perfectly on subsequent bars. However, this
is just a workaround, it doesn't solve what I regard as a bug. Can this be
fixed?