I wonder if this might have something to do with it...
If the subroutine's prototype is "($$)", the elements to be
compared are passed by reference in @_, as for a normal subrou-
tine.  This is slower than unprototyped subroutines, where the
elements to be compared are passed into the subroutine as the
package global variables $a and $b (see example below).
Maybe a prototype is being applied to the "borked" sub call?

In reply to Re^5: Sorting, recursion, and tail-call optimizations by kwaping
in thread Sorting, recursion, and tail-call optimizations by Limbic~Region

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