Polymorphic join, object.destroy issue

My generic routine looks like this:

def update_linked_poly_side(base_side, ids, poly_side)

get back the current linked items, and the base part

of the polymorphic field names, like ‘appllinkable’

linked, poly_base = self.polymorphic_info base_side
id_attr = base_side+’_id’
linked.each do |link|
linked_model_id = (link.send id_attr).to_s
link.destroy unless ids.include(linked_model_id)
ids.each do |id|
linked.create(blah blah blah - create works fine)

The link.destroy works fine for the first link that is currently
linked but isn’t in the ids list, but it doesn’t work for any
subsequent links that should also be destroyed.

Runtime logging (not in the code above for clarity) reports:
at entry,
3 appllink objects, ids [“3”, “1”, “2”] in linked (correct)
poly_base = ‘applinkable’ (correct)
ids = ["", “2”]
in the linked.each do |link| loop
it looks for “3” in ids, doesn’t find it and logs:
SQL (0.000694) BEGIN
Appllink Destroy (0.000345) DELETE FROM ‘appllinks’
WHERE ‘id’ = 9
SQL (0.001159) COMMIT

then it looks for “1” in ids, doesn’t find it and logs:
SQL (0.000138) BEGIN
SQL (0.000137) COMMIT

There isn’t an issue with the first linked item that is to be deleted,
but there isn’t a SQL statement generated for any subsequent items that
should be removed… adding new linked items works just fine (that’s in
the ids.each do |id| loop).

Any ideas? Anyone? Oh, and Rails 2.1.0, Ubuntu 8.04, Ruby 1.8.6

Curiouser and curiouser…

I changed the config.cache_store from :mem_cache_store to :file_store,
and the proper SQLs are generated for all the deletes.

Clearly I have some reading up on memcached to do… perhaps this was
tied up in some model caching I wasn’t aware that I was doing.