The drivers who are confused are those that use the right hand lane to go straight on. As it stands, according to the Highway Code, that lanes only for those turning back on themselves to head back to Cofton.
Rule 186 of the Highway Code is quite ambiguous when it comes to the scenario of going straight on at this roundabout (towards Dawlish). The problem is that theres no signage (roadside or on the road) to indicate which lane is the appropriate one. Merlins advice is what I always follow unless signage indicates otherwise.