SPConstraintLists unexpected key violation

[Alex]

Hi,

I am not sure how much support I can still get on this legacy SP element, but I will try my luck anyway.

I have installed SPConstraintLists add-on to WSS 3.0 site and defined a multi-column unique key for a custom list (template #100).
This site is intended for Model Number management of our hardware products, so I want to have the Model # field itself to be unique (to prevent duplicate model numbers) and I also need to have a combination of several fields to be unique to prevent someone entering a Model # with duplicate combination of features.

Therefore I have two unique keys defined:
- Model #
- Multi-field key

However, in the process of creating this custom list I had to change available drop-down choices for some look-up fields a few times and then I started getting some weird issues with the uniqueness of the fields:

1. It complained that "Found existing unique key values" when I tried adding a new item to the list, even though there was no such item in the list (it is possible that such item existed there before, but was later deleted before such unique key was defined)
2. I am able to create a duplicate item with all fields that are all part of a multi-field unique key being the same and I get no error

What I did so far:
I tried deleting the multi-field unique key and re-creating it again - no difference.
I tried de-activating and re-activating the feature for this site - no difference.
I tried deleting all keys, deleting all items in the list, then re-defining the keys and adding items back to the list - same issues as above (errors on supposedly violated uniqueness or ability to add duplicates)

Not sure what else to try next.
Any help is greatly appreciated, since I really don't want to write my own event handlers to ensure these conditions.

Thanks in advance!