VMware guest filesystem discovery - context macros do not work if OS is windows

In case I want to modify the default Template VM VMware Guest to create a trigger for free disk space and use a context macro in it, this does not work in case the OS is windows.
The key vmware.vm.vfs.fs.discovery returns

{#FSNAME}

with "\" in case it's a windows machine  ("C:\") and this is not supported by context macros (documented here

The trigger gets created, but becomes unsupported with error:

It should be possible to use full functionality of context macros in default templates.