How do I detect the currently installed features during a MajorUpgrade using WiX Burn MBA Bundles?

I'm using WiX 3.7's Burn/Managed Bootstrapper Application features to create a custom MBA-based installer. For each of the packages in my bundle's chain, when performing a MinorUpdate, I can easily detect which of the package features are already installed to ensure I maintain those feature selections during the upgrade by using these events provided in the WiX base class for the bootstrapper: DetectPackageComplete, DetectMsiFeature, DetectRelatedBundle, DetectRelatedMsiPackage, DetectComplete.

However, during a MajorUpgrade, I'm only seeing a way to determine which package(s) are installed, but am not seeing how to determine which features are installed, as the DetectMsiFeature event does not fire. I tried using the MigrateFeatures flag on the product's configuration, but that doesn't seem to work (or I'm not using it right).

What is the correct way to detect/migrate existing features when performing a MajorUpgrade using a Custom Managed Bootstrapper Application in WiX?

Some file snippets:

Note: I can provide a fully working VS Solution with all code if that is helpful.

Bundle.wxs:

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" xmlns:bal="http://schemas.microsoft.com/wix/BalExtension">
    <Bundle Name="Bootstrapper1"  Version="1.1.0.0" Manufacturer="Knights Who Say Ni" UpgradeCode="e6fbf160-d1d9-4b38-b293-94d60eae876f" Compressed="yes">    
        <BootstrapperApplicationRef Id="ManagedBootstrapperApplicationHost" >
          <Payload SourceFile="$(var.ManagedBootstrapperApplication.TargetPath)" />
          <!-- other files here -->
        </BootstrapperApplicationRef>
        <Chain>      
          <PackageGroupRef Id="NetFx40Web" />
          <MsiPackage SourceFile="$(var.SetupProject1.TargetPath)" EnableFeatureSelection="yes" Vital="yes"  Compressed="yes" />
        </Chain>
    </Bundle>
</Wix>

Product.wxs:

<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
    <Product Id="*" Name="SetupProject1" Language="1033" Codepage="1252"
           Version="1.1.0.0" Manufacturer="Knights Who Say Ni" 
           UpgradeCode="5fcd463a-3287-4fdf-bf00-d5d74baeccda">

        <Package InstallerVersion="200" Compressed="yes" InstallScope="perMachine" />
        <MajorUpgrade AllowSameVersionUpgrades="no" AllowDowngrades="no" MigrateFeatures="yes" DowngradeErrorMessage="Bring me a shrubbery!" />
        <MediaTemplate EmbedCab="yes" />

        <Feature Id="feature_one" Title="Primary Feature" Level="1">      
          <Component Id="CMP_emptyFile1" Guid="{1740AFA6-A98F-482A-B319-A153AA1BEF10}" Directory="INSTALLFOLDER">
            <File Id="file_emptyFile1" Checksum="yes" KeyPath="yes" Source="TextFile1.txt" />
          </Component>      
        </Feature>
        <Feature Id="feature_Two" Title="Optional Feature" Level="2">
          <Component Id="CMP_emptyFile2" Guid="{F0831C98-AF35-4F5E-BE9A-2F5E3ECF893C}" Directory="INSTALLFOLDER">
            <File Id="file_emptyFile2" Checksum="yes" KeyPath="yes" Source="TextFile2.txt"  />
          </Component>
        </Feature>    
    </Product>
</Wix>

CustomBootstrapper.cs

public class CustomBootstrapperApplication : BootstrapperApplication {        
    protected override void Run() {
            DetectPackageComplete += HandlePackageDetected;
            DetectMsiFeature += HandleFeatureDetected;
            DetectRelatedBundle += HandleExistingBundleDetected;
            DetectRelatedMsiPackage += HandleExistingPackageDetected;
            DetectComplete += HandleDetectComplete;
            this.Engine.Detect();
            //blocks here until DetectComplete fires...
    }

    private void HandleExistingPackageDetected(object sender, DetectRelatedMsiPackageEventArgs e) {
        Log(string.Format("Detected Related Package {2} ({1}) at version {3} which is a {0}",
            e.Operation, e.PackageId, e.ProductCode, e.Version));
    }

    private void HandleExistingBundleDetected(object sender, DetectRelatedBundleEventArgs e) {
        Log(string.Format("Detected Related {2} Bundle {0} at version {1} which is a {3}",
            e.ProductCode, e.Version, e.RelationType, e.Operation));
    }

    private void HandleFeatureDetected(object sender, DetectMsiFeatureEventArgs e) {
        Log(string.Format("Feature {0} from Package {1} detected in state {2}",
            e.FeatureId, e.PackageId, e.State));
    }

    private void HandlePackageDetected(object sender, DetectPackageCompleteEventArgs e) {
        Log(string.Format("Package {0} Detected in State {1}",
            e.PackageId, e.State));
    }

    private void HandleDetectComplete(object sender, DetectCompleteEventArgs e)
    { /* release the main thread to continue with work */ }

}

Output on upgrade:

Note that the package and two features were both installed at v1.0.0 and detected in state Absent. The Related Package was detected, but no feature details are included.

Detected Related Upgrade Bundle {5eff0a3c-4b0d-4fd9-875f-05117c07f373) at version 1.0.0.0 which is a MajorUpgrade
Package NetFx4OWeb Detected in State Present
Detected Related Package {540AE32D-75C0-4BF3-A72D-ADBE97FSFF3E} (SetupProject1.msi) at version 1.0.0.0 which is a MajorUpgrade
Feature feature_one from Package SetupProjectl.msi detected in state Absent
Feature feature_Two from Package SetupProjecti .msi detected in state Absent
Package SetupProject1.msi Detected in State Absent

Solution

DetectMsiFeature is telling you the state of features for the new package; it's not installed, so neither are the features. DetectRelatedMsiPackage gives you the data you need to query the feature states of the installed version using the (native) MSI API functions MsiEnumFeatures and MsiGetFeatureState/MsiGetFeatureUsage.