We have discussed this internally and it turns out that there is a security related product standard that doesn’t allow any service which might change the state of the system to be called without an XSRF token. What this means is that we cannot accept OData calls using the HTTP Get operation with the Query Templates in the Mode FixedQuery but can in the Mode of Query.
To use the Mode FixedQuery with the SQL templates you have to use the HTTP POST operation instead of HTTP Get.
Hope this helps to explain and we will update the help documentation accordingly.
Sam