UT_AutoInterrupt is misbehaving

[bamfbamf]

Hello,

I'm working on a big project which uses 3rd party library and I get some strange results if I try to interrupt my nodes. At first i thought that I'm doing something wrong and UT_AutoInterrupt send to callback of this library is not working properly, so I took example node that comes with Houdini SOP_Flatten, removed almost all code from cookMySop() and tried to interrupt it. This is what I get:

There should be only Warning set. But I do get additional Error. And I don't know from where it come from. This is the code I have in cookMySOp():
 

OP_ERROR
SOP_Flatten::cookMySop(OP_Context &context)
{
    OP_AutoLockInputs inputs(this);
    if (inputs.lock(context) >= UT_ERROR_ABORT)
        return error();

    auto progress = UT_AutoInterrupt("");    
    for (auto i = 0; i < 10000; i++)
    {
        if (progress.wasInterrupted())
        {            
            this->addWarning(SOP_MESSAGE, "Test interrupted.");
            return error();
        }

        std::cout << "YAY: " << i << "\n";
    }
    
    return error();
}

Anybody knows why I do get this additional Error state when interrupting the node?
I'm on H18.0.348.