The budgeting in Blanket Agreement and release can be done at two levels. Agreement - > Encumbrance, give the account for budgeting. or Leave it blank.
In case the organization chooses to perform encumbrance at release level and not agreement level, the encumbrance is happening upstream and has nothing to do with the BPA.
Please confirm if the amendment increased the value of the blanket release, amendment to terms or lowering the price is just about fine. But increasing the amount of the blanket release may be treated as a bug by Oracle Dev.
Yes system accepts to increase on amount. i agree if it reduce the amount than agreement can fine but increase on amount is something looks like bug on application.