Earned Value and Expenses Accrual types

I have used the search facility in the forum but can’t find a solution so I’m throwing open the problem.

When using the Activity Usage Spreadsheet;-
We have a task some weeks long with an expense cost loaded and its accrual type set to "Start Of Activity". This has been baselined thus. So, you would expect that should this task be progressed as say, 50% (Physical or otherwise) starting on it’s planned start date and the status date at the same percentage through the task that the Planned Value and Earned value would be the same as normal. Well, you would wouldn’t you?

But you don’t....

Planned Value is correct in that all the Cost should have been accrued but the Earned Value is showing 50% (in the above case) of the value. This is bobbins! The cost should have happened, the Actual shows this to be true but the EV data is flawed. This translates to any reports run on this data.

Interestingly, the column data in the Activity Table for Planned Value Cost and Earned Value Cost show the correct data.