Overview:
Order fails to reopen after being opened/closed and the expense class was changed.

Steps to Reproduce:

1. Create an order and an order line with an expense class

2. Open the order

3. Unopen the order

4. Change the expense class

5. Open the order

Expected Results:
Order is opened.

Actual Results:
500 - "Error retrieving the transactions"

Additional Information:
Removing the fund distribution and saving also generates the same error.

The issue comes from the pending to pending encumbrance strategy removing the old encumbrance without updating the fund distribution link to it.

The same issue does not happen when the expense class is changed in an opened order: in this case, the encumbrance link is updated. The reason for the difference is that the fund distribution's encumbrance link is only updated when a new encumbrance is created, and new encumbrances are not created for pending orders.
Interested parties: