Unexpected conversion from 'true'/'false' to some integer types

[jboelterintc]

Unexpected conversion from 'true'/'false' to some integer types

[jshastid]

I am having the same issue and apologies if I am not understanding this correctly as I am new to C++ and have only just started using this library, but it looks like the integer value is not being considered a basic_json and so is calling the explicit cast from_json. At least the comment above the function leads me to believe this.
// overload for arithmetic types, not chosen for basic_json template arguments
// (BooleanType, etc..); note: Is it really necessary to provide explicit
// overloads for boolean_t etc. in case of a custom BooleanType which is not
// an arithmetic type?