Collections intermittent problem

Question

Hi there
I am experiencing some strange behaviour with collections.
I have a page 1 where you add items to a collection via a checkbox and a submit button. The checkboxes appear checked when the item is already in the collection - this is done in the select as follows:
select
APEX_ITEM.CHECKBOX(2, dcd.dcd_id,DECODE(dcd.dcd_id,(select c001 from
htmldb_collections where c001 = dcd_id and collection_name =
'FYP_CART'),'CHECKED',null)),
Page 2 shows a simple collection report.
(no joins, simply 'select c001,c002...from apex_collections
WHERE collection_name = 'FYP_CART')
Here's the intermittent problem..
I add 5 items (for example) on page 1, and receive a message that 5 items have been added.
When I then go to the report page 2, it shows only 4 items in the collection.
If I then go back to page 1, there are 5 checkboxes checked, which proves that there are 5 items in the collection.
So, im at a loss to understand what is going on here, seems to be a bug?
Most of the time it works perfectly, but occasionally does this. Often also after removing an item from the collection, I am then unable to add the same item.
Has anyone else seen anything like this?
Thanks for your time,
Rhodri

Answer 1

Forgot to mention...
I am using Apex 2.2.1
I am capturing the SEQ_ID during the add member, as follows:
:P3_X := HTMLDB_COLLECTION.ADD_MEMBER(
p_collection_name => 'FYP_CART',
p_c001 => v_dcd_id,
The 'Add member' returns the next valid sequence number, so appears to work, but it doesnt always go into the collection.
very strange.