Hi Oscar,
The system behaviour is correct. If you notice on your TPM44 screenshot, the no of days used for Update type AD1000 is -14. in your posting log a negative amount would have been posted.
Here is the logic:
Your Purchase has a Position Value Date of 30 April and payment date of 4th May. So the accrued Interest to pay is paid to the seller actually till 4th May. So Period Between 30th April and 4th May, the system will try to post a Negative amount in order to balance the interest paid till 4th May.
If you do the accrual for next period and compare, the net amount accrued will be correct.
Regards,
Nikhil