Staff.instr code change?

[Kieren MacMillan]

Hello, all --

Per the thread on the user list... Has the code for Staff.instr  
changed between 2.6 and 2.8 -- specifically, \set Staff.instr does  
not appear to work after the music has begun, e.g.

        \relative
        {
                \set Staff.instr = "one"
                c d e f g
                \set Staff.instr = "two"
                a b c d ...
        }

will always show "one" as the instr.

In the chamber opera I'm frantically trying to finish and engrave  
[ =) ] , I definitely need the ability for my flute player to take  
piccolo, clarinet to take b.cl., violin to take viola, etc., and for  
the score to display the correct instr.

What is the best workaround or fix for this issue?

Thanks,
Kieren.