It means to Preserve file attributes, and modification time as gzip/bzip do. For some reason the modification doesn't get preserved although in my test it worked. Even changing it before closing file worked (test/2). Maybe someone can spot the problem and fix that.
I found a minute to check that with strace and found an error and also problem with system (?) write buffer that was writing right before closing but after set_fstat(). Forcing flush solved it.
Preserve file attributes, and modification time
It means to Preserve file attributes, and modification time as gzip/bzip do. For some reason the modification doesn't get preserved although in my test it worked. Even changing it before closing file worked (test/2). Maybe someone can spot the problem and fix that.