Mike, it turns out it really does not depend whether you’re holding a free bus pass of other councils under English National Concessionary Travel Scheme.
If you merely holding Disabled Railcard added to your Oyster, your journey details will end up like what Mike the admin suggested and you will not be capped because your total fare has not reached the Off-peak Railcard Daily cap of £8.90, rather you will be capped for bus journeys at £4.65 and have the fare of the solitary tube ride on top of that.
If you do hold a free bus pass under the English National Concessionary Travel Scheme, your bus journeys would be free after 0900 as mentioned here: https://tfl.gov.uk/transport-accessibility/fares-and-tickets In this case only bus journeys before 0900 would be charged via your Oyster, which under Hopper Fare would amount to £1.55 only.