Previously, they were registered, then forgotten. This means that each time
the start swap view was run, another receiver was registered. As a result,
they were being invoked multiple times.
It doesn't appear that this had any specific side effects which were terrible,
but they definitely have the potential to going forward.
Note that because we are not using `Fragments` with their convoluted, but at
least well documented API, I'm not 100% certain that I've unregistered the
receivers at the right location.
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