Installer (wix built msi) does not remove a feature element (a directory) during uninstallation

Question

I am having issues getting my installer (msi) to remove a feature based component during uninstallation. The feature element, as per below, contains conditional component group references, which are to a directory id and a number of other components in another fragment (e.g., iis:WebAppPool):

Product.wxs

    <Feature Id="StandardIntegration" Level="1" Title="StandardIntegration">
  <ComponentGroupRef Id="SERVICES"/>
  <!-- Integration Services IIS -->
  <ComponentRef Id="comp1"/>
  <ComponentRef Id="comp2"/>
  <ComponentRef Id="comp3"/>
  <ComponentRef Id="comp4"/>

  <Condition Level="0">
  <![CDATA[HAS_FEATURE_SET <> "true"]]>
</Condition>
</Feature>

OtherFragment.wxs

<DirectoryRef Id="INSTALLDIR">
  <Directory Id="InstancePath">
    <Directory Id="SERVICES" Name="Services"/>
  </Directory>
</DirectoryRef>

<Component Id="comp1" Directory="SERVICES" Win64="yes" KeyPath="yes" Guid="$(var.c)" MultiInstance="yes" Shared="no">
  <iis:WebAppPool Id="wbpoolid" ManagedRuntimeVersion="v4.0" Name="CMP_[NAME]" User="AppPoolUser" Identity="other" RecycleMinutes="0" RecycleRequests="0" ManagedPipelineMode="integrated">
  </iis:WebAppPool>

....

All other components referred (including the ones that contains the iis web app pool element) are removed correctly during uninstallation, but the directory ("SERVICES") is not... and it's the only file directory that's not being removed. (E.g., all other files installed by the msi are being correctly removed.)

Any help would be much appreciated, thanks!