Budget exceeded in case of PR with multiple account assignment.

When we are creating PO from PR having multiple account assignments,
like
2 assets, the budget is getting zeroed out.

1. Assign budget to an internal order.
2. Create a PR with the above IO and assign 2 assets to it.
3. The result is "available amount of the budget is getting reduced by
the PR amount".
4. So if budget is of 50000 THB and PR is also of 50000 THB, then when
creating a PO there is no budget available.