When reading the ParamTypes of function types an array with the correct number of elements is returned, but all returned types have 0x0 handles. These lines reproduce the issue:
var returnType = LLVMTypeRef.Int8;
var parameterTypes = new[] {LLVMTypeRef.Double};
var functionType = LLVMTypeRef.CreateFunction(returnType, parameterTypes);
Debug.Assert(parameterTypes.First() == functionType.ParamTypes.First()); // Fails