I suppose the problem you're experiencing is not really a bug but due to the fact that a slice on the stash deliveres globs not values:

  DB<1> ($a,$b)=qw/A B/
 
  DB<2> @n=qw/a b/
  
  DB<3> @save=@::{@n}
 
  DB<4> x @::{@n}
0  *main::a
1  *main::b
  DB<5> x @save
0  *main::a
1  *main::b
[download]

initializing the localized vars should be done with the _values_ not with the globs. In this way you are "re-aliasing" the package vars to the old ones!

But I'm not enough of a perl4 expert for details... ;)

UPDATE: to be more precise, your code above should be equivalent to something like

local (*a,*b) = (*a,*b)

and not

local ($a,$b) = ($a,$b)