Azure Cloud Service does not pass runtime environment variables to startup tasks - azure

Question

I have created a Cloud Services definition with several start-up tasks. I have a common set of Environment variables that I want to be available from each task, for example if it's running in the emulator. For that I used the the following documentation: https://azure.microsoft.com/nl-nl/documentation/articles/cloud-services-startup-tasks-common/#differentiate-between-running-in-the-emulator-and-the-cloud
The problem is that I do not get any variables from the runtime block passed into my tasks. Any variables declared at the task level are passed normally.
My definition looks like this:
<?xml version="1.0" encoding="utf-8"?>
<ServiceDefinition name="Portal.CloudService" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition" schemaVersion="2015-04.2.6">
<WebRole name="Portal" vmsize="Small">
...
<LocalResources>
<LocalStorage name="StartupLog" sizeInMB="100" cleanOnRoleRecycle="false"/>
</LocalResources>
<Runtime>
<Environment>
<Variable name="ComputeEmulatorRunning">
<RoleInstanceValue xpath="/RoleEnvironment/Deployment/#emulated" />
</Variable>
<Variable name="CurrentEnvironment">
<RoleInstanceValue xpath="/RoleEnvironment/CurrentInstance/ConfigurationSettings/ConfigurationSetting[#name='Environment']/#value" />
</Variable>
<Variable name="StartupLogPath">
<RoleInstanceValue xpath="/RoleEnvironment/CurrentInstance/LocalResources/LocalResource[#name='StartupLog']/#path" />
</Variable>
<Variable name="testvar" value="test"/>
</Environment>
</Runtime>
<Startup>
<Task commandLine="AddCertToTrustedRootCA.cmd" executionContext="elevated" taskType="simple" />
<Task commandLine="ConfigureIIS.cmd" executionContext="elevated" taskType="simple">
<Environment>
<Variable name="taskvar" value="test"/>
</Environment>
</Task>
</Startup>
...
</WebRole>
</ServiceDefinition>
I'm debugging ConfigureIIS.cmd at the moment. I get passed the %taskvar%-variable defined at task level, but the runtime variable %testvar% is not available, like all the other runtime environment variables.
What I have tried so far:
Set only the most simple variable (%testvar%) and remove the RoleInstanceValue variables
Set the <Runtime>-element to <Runtime executionContext="elevated"> to match the tasks execution level
Remove the executionContext from the tasks
As far as I can see my code is equal to the example as given by Microsoft and yet it does not work. Did I make a mistake in my definitions, or am I missing something?