In my work on bug 454829, I create collections for specific sets of messages. Some changes to these messages, such as tag changes, do (mostly) generate onItemsModified events, although there is some loss there which asuth has seen. Some modifications, such as starring or marking a message read/unread, do not generate onItemsModified events. The proximal cause is that the test in GlodaCollectionManager:itemsModified that reads: if (collection.query.test(item)) returns false. I don't know why.

It turned out the collection and its query were being garbage-collected but the temporary query created by the indexer resulted in debug output that looked like the query was still around and just broken. We should probably create a "gloda debugger helper" extension that has, as one of its many features, the ability to see the "live" collections (and queries) from the gloda cache perspective. It would force a heroic GC before refreshing the list too.