Adblock Plus 2.4 (but reproducible at least as far back as 2.1.2), SeaMonkey 2.21.
Steps to reproduce:
1) Open blockable items
2) Switch tabs
Expected results: Blockable items will change, showing only those for the new tab.
Actual results: Blockable items window continues to reflect the tab on which it was opened. To get blockable items for the new tab, it's necessary to manually close and reopen the blockable items window.
I might be able to suggest a patch if someone can explain to me what is happening "under the hood" that is causing this bug.