New Inconsistency - Shell Cottage

[Steve]

No: HPFGUIDX 176317

When Harry, Ron, Hermione, etc... arrive at Shell 
Cottage, Bill informs them that there is a Secret Keeper
charm on the place. Yet, Ron mentions it earlier, 
actually mentions Shell Cottage a couple of times,
and when Harry arrives with Dobby, Harry can see the
cottage in the distance. 

Are we seeing a mistake or are we seeing a new variation
of the Charm. Are there aspect of the Fidelius Charm that
we are unaware of, or did JKR simply over look a few 
details. 

For the record, mistake or not, it didn't distract
from my reading at all. I'm on my fourth read and just
now noticed it.

Steve/bboyminn