i thought this may have been a difference in your version of rc and the one i was using. now i don't think so.
; 9fs sources ; exec /n/sources/plan9/386/bin/rc ; a=(1 '2 3' 4 5) ; s a ; whatis a a=('2 3' 4 5) ; s a ; whatis a a=(4 5) ; s a ; whatis a a=5 ; s a ; whatis a a: not found - erik