Weak hash tables are too strong?

[Neil Jerram]

In the following example, can anyone explain to me what is preventing
the vector #(2 3 4) from being GC'd?  Or am I misunderstanding how
weak hash tables are meant to work?

guile> (define b (make-doubly-weak-hash-table 7))
guile> b
#w(() () () () () () ())
guile> (begin (hash-set! b 2 (vector 2 3 4)) 3)
3
guile> b
#w(() () ((2 . #(2 3 4))) () () () ())
guile> (gc)
guile> b
#w(() () ((2 . #(2 3 4))) () () () ())
guile> (gc)
guile> b
#w(() () ((2 . #(2 3 4))) () () () ())
guile> 

Thanks,
        Neil