binding reference to scalar types: shouldn't it work already?

Hello,
I'm trying to bind a reference to a bool. This thing compiles:

     globals(L)["dotrap"] = boost::ref(dotrap);

but at compile time I get the following exception:

     terminate called after throwing an instance of 'std::runtime_error'
       what():  Trying to use unregistered class

It looks like that luabind is treating a reference to a bool as a user 
defined type. So... it isn't able by default to bind references to 
simple bools?
By the way, luabind does know about bool, in fact I can do

     globals(L)["dotrap"] = dotrap;

but here I create a copy of the value, which is not what I want to do.

Cheers.

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