WiX 3.6 Burn bootstrapper fails to elevate

I'm somewhat new to the world of WiX, so it's very possible I've missed something very obvious.

I've installed WiX 3.6 beta, and grabbed the source as well to work from (and adjusted it to use the WiX 3.6 installed binaries), but I'm having problems with the bootstrapper. I can get my custom UI to display, but it won't install anything - it fails with the following in the logs.

Error 0x80070006: Failed to write message type to pipe.
Error 0x80070006: Failed to write send message to pipe.
Error 0x80070006: Failed to send BURN_ELEVATION_MESSAGE_TYPE_EXECUTE_DEPENDENCY message to per-machine process.
Error 0x80070006: Failed to register the dependency on per-machine package.
Error 0x80070006: Failed to execute dependency action.
Error 0x80070006: Failed to execute apply.

The same thing happens if I use the WixUX in WiX source. If I (manually) run it as administrator, it'll install the file using either my GUI or WixUX. If I use the default WixStandardBootstrapperApplication, it installs fine regardless of the elevation.

The MSI file itself currently installs into UserData, so it doesn't actually need elevation.

My Bundle.wxs looks like:

<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi" xmlns:util="http://schemas.microsoft.com/wix/UtilExtension">
    <Bundle Name="MahChats" Version="1.0.0.1" Manufacturer="MahApps" IconSourceFile="../../../MahChats/src/MahChats/mahchats.ico" UpgradeCode="9c9a0cf4-659f-4543-b05a-962322fec4a0">
        <BootstrapperApplicationRef Id="ManagedBootstrapperApplicationHost">
            <Payload SourceFile='WixUX.dll' />
            <Payload Name='BootstrapperCore.config' SourceFile='WixUX.BootstrapperCore.config' />
        </BootstrapperApplicationRef>
        <Chain>
            <PackageGroupRef Id="Netfx4Full"/>
            <MsiPackage Id='MahChats' Vital='yes' Name='MahChats.Setup.msi' SourceFile="C:\Code\mahchats\src\MahChats.Setup\bin\Debug\MahChats.Setup.msi" />
        </Chain>
    </Bundle>
    <Fragment>
        <WixVariable Id="WixMbaPrereqPackageId" Value="Netfx4Full" />
        <WixVariable Id="WixMbaPrereqLicenseUrl" Value="NetfxLicense.rtf" />

        <util:RegistrySearch Root="HKLM" Key="SOFTWARE\Microsoft\Net Framework Setup\NDP\v4\Full" Value="Version" Variable="Netfx4FullVersion" />
        <util:RegistrySearch Root="HKLM" Key="SOFTWARE\Microsoft\Net Framework Setup\NDP\v4\Full" Value="Version" Variable="Netfx4x64FullVersion" Win64="yes" />
        <PackageGroup Id="Netfx4Full">
            <ExePackage Id="Netfx4Full"
                Cache="no"
                Compressed="no"
                PerMachine="yes"
                Permanent="yes"
                Vital="yes"
                SourceFile="dotNetFx40_Full_x86_x64.exe"
                DownloadUrl="http://go.microsoft.com/fwlink/?LinkId=164193"
                DetectCondition="Netfx4FullVersion AND (NOT VersionNT64 OR Netfx4x64FullVersion)" />
        </PackageGroup>
    </Fragment>
</Wix>

I've not really found any documentation on Burn, so I'm using the WixUX project to nut it out, and I'm using Bootstrapper.Engine.Plan(LaunchAction.Install); to attempt the install.

Paul, that is a bug. There were a bunch of fixes to dependency code over the holidays that very likely fixed this issue. Unfortunately, there is not a weekly build out due to issues with SourceForge that I'm working right now (literally). I expect a build out next Friday and encourage you to move to it as soon as it is available.