Raster maps not working on 28.20 :(

After updating to 28.20 the raster maps that previously worked flawlessly will no longer display. I can see them there in the map list on the device, but selecting / deselecting doesn't have any effect any more. I've also tried deleting and re-adding them.

Is this a conscious decision, or something that will likely be corrected in a future update - this was one of the main issues for purchasing this device, so it will be a huge blow if they can not longer be used!!

Thanks.