Rendering of lakes on Garmin devices

I recently downloaded a map of the United Kingdom from http://garmin.openstreetmap.nl/ and installed it on an Etrex 30. I found that lakes and ponds (e.g. https://www.openstreetmap.org/#map=17/50.80484/-1.18653) do not render in blue as they used to. I also noticed that when the cursor is left on a blank area of the map, it is identified as 'Great Britain', which is also new behaviour. The same problem occurs on a Garmin Colorado, and occurs with much larger lakes (e.g. Windermere). A map downloaded from the same site in January renders correctly on Garmin devices, and the map still renders correctly on the OSM website. I asked a similar question a long while ago (https://help.openstreetmap.org/questions/12148/rendering-of-lakes), and some helpful people told me about multipolygon relations, which fixed the problem. Has an entity called 'Great Britain' recently been created, and is the Garmin rendering engine seeing it as a kind of land use? Sorry, I'm guessing, but I cannot see how to fix the problem.

Additional information: While trying to determine whether the problem is in the OSM data, the preparation of the downloaded Garmin 'img' file or the Garmin GPS software, I found that the 'img' file renders correctly in BaseCamp. Unfortunately I do not know enough about map rendering to determine where the fault lies. Can anyone help?