Event Sender Gets Disposed In Client's Event Handler Code

Answer 1

Seems to me that there's a lot of things happening at the same time to keep proper track of.

I would try to separate the "disposal of objects" concern, for example add to-be-disposed items in a queue/disposal manager of some sort which would process (call Dispose on) items in a safer and more well designed/understood and deterministic way. If anything, this should help with debugging the problem.

Answer 2

You might consider a different approach if you just need a single listener that should dispose an object, perhaps a simple callback (implementing the Begin/End pattern in .NET).

Disposing of an event's sender isn't ever semantically appropriate: the object that created the collection (or initiated its creation) should be responsible for disposing of it, not an arbitrary observer.