Windows 8 Task Scheduler will not run "At system startup" task

[Peter Binney]

I have moved to Windows 8 from XP where "on startup" tasks worked fine.
In Windows 8 I can't for the life of me get one to run. I add it through the UI and have Enable Tasks History set, but it never runs and there are no errors in the Event Log.
The task is (for now) just to run a test .bat script, and is defined as:

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.4" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
<RegistrationInfo>
<Date>2013-01-05T11:04:13.4996188</Date>
<Author>JCPR-Dell-3\peter</Author>
</RegistrationInfo>
<Triggers>
<BootTrigger>
<Enabled>true</Enabled>
<Delay>PT10S</Delay>
</BootTrigger>
</Triggers>
<Principals>
<Principal id="Author">
<RunLevel>HighestAvailable</RunLevel>
<UserId>S-1-5-18</UserId>
</Principal>
</Principals>
<Settings>
<MultipleInstancesPolicy>IgnoreNew</MultipleInstancesPolicy>
<DisallowStartIfOnBatteries>true</DisallowStartIfOnBatteries>
<StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
<AllowHardTerminate>true</AllowHardTerminate>
<StartWhenAvailable>false</StartWhenAvailable>
<RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
<IdleSettings>
<StopOnIdleEnd>true</StopOnIdleEnd>
<RestartOnIdle>false</RestartOnIdle>
</IdleSettings>
<AllowStartOnDemand>true</AllowStartOnDemand>
<Enabled>true</Enabled>
<Hidden>false</Hidden>
<RunOnlyIfIdle>false</RunOnlyIfIdle>
<DisallowStartOnRemoteAppSession>false</DisallowStartOnRemoteAppSession>
<UseUnifiedSchedulingEngine>false</UseUnifiedSchedulingEngine>
<WakeToRun>false</WakeToRun>
<ExecutionTimeLimit>P3D</ExecutionTimeLimit>
<Priority>7</Priority>
</Settings>
<Actions Context="Author">
<Exec>
<Command>cmd</Command>
<Arguments>/c E:\utils\cy-test.bat arg1 arg2</Arguments>
</Exec>
</Actions>
</Task>

The scheduler task is running (other tasks run and show history).

I have tried without and with the "<Delay>PT10S</Delay>".

What on earth is (not) going on?

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