Ice.Default.Locator and stand-alone IceBox service

I am developing a C# IceBox service which accesses some well-known objects on our production IceGrid, and so when I am developing I set

Ice.Default.Locator=IceGrid/Locator:tcp -h gridnode1 -p 4061

in my config.servicenet file.

However, after I have set up all my servant objects for the service, and come to call

_adapter.activate()

I get an Ice.UnknownException, containing an "Ice::AdapterAlreadyActiveException" lurking within the "unknown" field.

This is thrown line 1211 of ObjectAdapterI.cs

locatorRegistry.setAdapterDirectProxy(_id, proxy);

The value of locatorRegistry is:
{IceGrid/LocatorRegistry-Master -t:tcp -h gridnode1 -p 3911}

Now -- I have a workaround for development, which is to call:

_adapter.setLocator(null);

prior to activation; but I need to comment this line out prior to deploying the IceBox service via IceGrid, since it causes problems otherwise.

Could anyone give me a hint as to what might be happening, and how I may run the same code in development and on the grid without needing to call this setLocator workaround? Many thanks!