OK, here's the problem.
In the existing course we can delete and add sentences but we can't delete words or phrases. We've tried in the past to get round this problem by disabling all the sentences associated with an erroneous word/phrase but the system doesn't like this and it continues to generate the sentences.
In the new course we've made these revisions and when it's released there should not be erroneous words/phrases.
There is an added complication to this particular phrase. 'Rheolaeth bell' does mean 'remote control' in the context of controlling something from a distance, not the actual device.
So I'm going to change the sentences to refer to the correct meaning of this phrase for now.