Subscribe/Unsubscribe link doesn't work correctly with multiple subscriptions

The AJAX subscription UI just very successfully confused me. It does things horribly wrong if I have both an implicit subscription and one via a duplicate.

I browsed to bug #109153, where the subscribers portlet showed correctly showed that I had an implicit subscription (via launchpad-project). It didn't, however, show what was causing the confusing behaviour - my additional subscription through a duplicate.

The green link at the top of the portlet said 'Unsubscribe'; I didn't think it was meant to do that for implicit subscriptions. I click on it, to see what happens - it immediately says 'Subscribing' (not 'Unsubscribing'), and... directly subscribes me to the bug. It even correctly JavaScripts me into the list of subscribers.

The link still says 'Unsubscribe'. If I click it, it unsubscribes me from the bug, removes me from the portlet, and the link changes to 'Subscribe', as expected. I can click that, and it will resubscribe me as normal.

If I now refresh the page, I have three subscriptions to the bug - one direct, one through a duplicate, and one through launchpad-project. The link is 'Unsubscribe', as expected.

On one occasion, clicking the 'Unsubscribe' link on the refreshed page caused it to try to subscribe me again, so it added me to the portlet a second time. I was only able to reproduce this twice.

Other times, clicking the link successfully unsubscribes me, removes me from the portlet, and changes the link to 'Subscribe'. But when I refresh the page, it goes straight back to 'Unsubscribe'.

Confused yet? I am. To add to the confusion, the portlet doesn't show me as being subscribed through a duplicate unless I'm also subscribed directly. But once I am subscribed directly, the subscription through launchpad-project vanishes.