WiX installing unselected features - wix

Question

I'm in the process of using WiX to create an install package with multiple features. It's using the Mondo UI to allow the user to select one or more features to install. The problem I'm having is that it's always installing all features, regardless of what the user selects.
Below is my WXS file:
<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
<Product Id="*" Name="Setup Test 1" Language="1033" Version="1.0.0.0" Manufacturer="dbush" UpgradeCode="MYGUID="yes" InstallScope="perMachine" Comments="testing the installer" />
<MajorUpgrade DowngradeErrorMessage="A newer version of [ProductName] is already installed." />
<MediaTemplate />
<Feature Id="all" Title="all features" Description="everything" Level="1" Display="expand">
<Feature Id="file1" Title="file1" Description="file1.txt" Level="1">
<ComponentGroupRef Id="file1" />
</Feature>
<Feature Id="file2" Title="file2" Description="file2.txt" Level="10">
<ComponentGroupRef Id="file2" />
</Feature>
<Feature Id="regkey" Title="registry key" Description="registry properties to install" Level="11">
<ComponentGroupRef Id="regkey" />
</Feature>
</Feature>
<Property Id="PROP1" Value="replacement" />
<UIRef Id="WixUI_Mondo" />
<UIRef Id="WixUI_ErrorProgressText" />
</Product>
<Fragment>
<Directory Id="TARGETDIR" Name="SourceDir">
<Directory Id="ProgramFilesFolder">
<Directory Id="INSTALLFOLDER" Name="setup_test_1" />
</Directory>
</Directory>
</Fragment>
<Fragment>
<ComponentGroup Id="file1" Directory="INSTALLFOLDER">
<Component Id="file1.txt" Guid="MYGUID">
<File Id="file1.txt" Source="src/file1.txt" />
</Component>
</ComponentGroup>
<ComponentGroup Id="file2" Directory="INSTALLFOLDER">
<Component Id="file2.txt" Guid="MYGUID">
<File Id="file2.txt" Source="src/test2.txt" />
</Component>
</ComponentGroup>
<ComponentGroup Id="regkey" Directory="INSTALLFOLDER">
<Component Id="reg_key_1">
<RegistryValue Root='HKCU' Key='SOFTWARE\setup_test_1\properties'
Name='prop1' Value='[PROP1]'
Type='string' />
</Component>
</ComponentGroup>
</Fragment>
</Wix>
What could be causing this?
I'm using WiX toolset 3.11.2 and Visual Studio 2017.

Answer 1

This was caused by the main Feature element having Id="all". Changing it to some other string such as "everything" allowed for individual features to be installed.
I wasn't able to find any documentation on why an Id with this name is a special case.