isBusesLayoutSupported and Reaper bug causes strict stereo out?

Audio Plugins
1

Hello,

I have the following code for my isBusesLayoutSupported- essentially I want to enforce a first order ambisonic input, and allow for only certain sizes of output for the main output bus. I also have four aux buses that I am enforcing be stereo.

bool MV360AudioProcessor::isBusesLayoutSupported(const BusesLayout& layouts) const
{
    const int mainOutputBusesChannelNum = layouts.getMainOutputChannels();
    const int outputBusCount = static_cast<int>(layouts.outputBuses.size());

    const auto& requestedMainIn = layouts.getMainInputChannelSet();

    if (requestedMainIn.isDisabled() || requestedMainIn != juce::AudioChannelSet::ambisonic(1))
        return false;

    // Only allow main output widths 2, 6, 8, 10, or 12.
    const bool isMainOutputSupported =
        (mainOutputBusesChannelNum == 2
         || mainOutputBusesChannelNum == 6
         || mainOutputBusesChannelNum == 8
         || mainOutputBusesChannelNum == 10
         || mainOutputBusesChannelNum == 12);

    if (!isMainOutputSupported)
        return false;

    // Hosts may temporarily disable aux buses during layout probing.
    for (int outputBusIndex = 1; outputBusIndex < outputBusCount; ++outputBusIndex)
    {
        const auto& outputSet = layouts.getChannelSet(false, outputBusIndex);
        if (!outputSet.isDisabled() && outputSet != juce::AudioChannelSet::stereo())
            return false;
    }

    return true;
}

I have an issue however when trying to instance my plugin in Reaper, that it does enforce 4 channel input in, BUT does not allow for my main bus input to be anything larger than 2 channels wide. Even when I request in the routing matrix to increase bus size to 6/8/10 or 12. However, if I only limit my main output bus sizes to be 6/8/10/12, I do not have this problem, and I am able to resize my output bus to 6/8/10/12. I also find that if I allow all input sizes, not just four wide for first order ambisonic, I do not have this issue.

TLDR- Why does it seem like limiting input channel set enforces stereo output as my main bus, even when I allow for other valid sizes for my main bus?