Items are not rescheduled after host monitoring changes on server

1. create item with short polling delay (for example system.uptime with 1s delay)
2. observe that data is gathered every second
3. disable host and reload configuration cache
4. observe that data is not gathered
5. enable host and reload configuration cache
6. observe that data is not gathered

Expected: data gathering is restarted after after host is enabled and configuration cache is reloaded.

Similar problem when assigning host to proxy and unassigning from it.