repeated time signatures

[Urs Liska]

The NR (1.2.3 "Displaying Rhythms") states that time signatures "are 
printed at the beginning of a piece and whenever the time signature 
changes."

But if I write

music = {
  \time 3/4
  R2.*4
  \time 3/4
  R2.
}

the time signature is printed a second time although it doesn't change 
(to my understanding)

a) Is this intended behaviour? And if yes, shouldn't it be documented?
b) How can I achieve that the time signature is only printed if it is 
actually different from the one currently in use?
c) How can I achieve the same (only displaying if really changed) for 
key signatures and clefs?

(Background: I have a piece with _lots_ of segments that are 
concatenated (in order to have music variables of manageable length that 
can easily be edited by different people. To make the source files more 
explicit I want each variable definition to start with \key \time and 
\clef commands.)

Thanks
Urs