Metrics for flowlet's pending is considering old events (prior to truncate)

To reproduce:
Send 1000 events to a stream, which are consumed by a flow.
Then, after flowlet processes these, delete the app.
Truncate the stream.
Redeploy the app.

At this point, the stream-consuming flowlet shows 0 'pending' events (on the flow UI).
Send 1 event into the stream, and the consuming flowlet will show 1000 'pending' events, whereas it should only show 0 or 1 pending event.