Cannot set data type for variables in Guide Template language

According to the documentation you should be able to set the data type of a variable using a kind parameter:

• N - number
• C - currency
• D - date

For example:

{{example [kind=N]}}

or

{{example [k=N]}}

However, we can't get this to work.

In our JSON object we have an order summary object:

   "Order Summary":{  
      "Order Sub Total":120.00,
      "Total Loyalty Discount":12.00,
      "Total Coupon Amount":5.00,
      "Total Shipping Amount":0.00,
      "Total Order Amount":130.00,
      "Total Tax Amount":1.30
   }

If I include the tag {{[Order Sub Total]}} it's rendered as 120.

I have tried using:

{{[Order Sub Total] [k=C]}}

and

{{[Order Sub Total] [kind=C]}}

But the decimal places are not displayed.

I've also tried [k=N] but that doesn't work either.

We've managed to work around this issue by using GTL in combination with AMPscript:

{{.datasource totals type=nested}}
  {{.data}}
    {"target":"order.[Order Summary]"}
{{/data}}
%%[
SET @sub = FormatNumber(TreatAsContent('{{[Order Sub Total]}}'), "C2", "en-AU")
SET @lld = FormatNumber(TreatAsContent('{{[Total Loyalty Discount]}}'), "C2", "en-AU")
SET @coup = FormatNumber(TreatAsContent('{{[Total Coupon Amount]}}'), "C2", "en-AU")
SET @sr = FormatNumber(TreatAsContent('{{[Total Shipping Amount]}}'), "C2", "en-AU")
SET @tot = FormatNumber(TreatAsContent('{{[Total Order Amount]}}'), "C2", "en-AU")
SET @ta = FormatNumber(TreatAsContent('{{[Total Tax Amount]}}'), "C2", "en-AU")
]%%
{{/datasource}}

We then display the AMPscript variable in the email. This works, but I'm keen to find out if the variable data type feature is broken or whether my syntax is incorrect.