Having had time to give this further thought, I'm wondering if labels etc are needed at all in the collections map? Just seeing the route lines would arguably be sufficient. The labels make the map appear cluttered and it's easy enough to see them by opening an individual route. Perhaps the default for labels in the collections map could be 'off' with the option to switch them one in the usual way.
Thanks for reporting that Martyn, it does look like a bug, so it'll need further investigation.
On opening the route collection display, all of the routes are shown on the map. There is a slider to turn them all off and individual sliders to turn the display of individual routes back on. Currently, the 'all off' slider works as expected but selecting an individual slider turns that route on but also displays the lables etc for all routes.
This collection is a good example: