If a user finds they are unable to turn off their Out of Office Alert after setting it on Domino Web Access in version 8.0 the below fix from IBM Notes Forum can correct the affected Agents behaviour.

1. Run “tell amgr sched” on all the servers in the Domain in order to verify in what database (mail\.nsf) is running the Out Of Office agent.
2. Open the database with the problem (mail\.nsf) from the Domino Administrator.
3. Go to –> View –> Design. At this point the Lotus Domino Designer will be opened with the database selected.
4. Expand the Code section from the left side menu and double click in Agents.
5. Select the OutOfOffice agent from the list.
6. Click in Disable button and close.
7. Verify again the Out Of Office agent from the server console executing: “tell amgr sched”.
At this point, the Out Of Office for this specific client will be disabled.

Edit: The forum link no longer works and therefore has been unlinked –