What a strange situation indeed!

The roundabout is normally only used by residents of the 3 houses to get to/from their houses.  But it looks like there is something illegal because the roundabout is not posted when coming from the north: cyclists riding contraflow will not know they are entering a roundabout.  Perhaps something to report to FixMyStreet.

Thanks for the pictures, I added oneway:*=no for [bicycle|speed_pedelec|mofa] and added the roundabout.