In a consortia, libraries need to be able to create budgets that cannot be edited by other libraries. However, the permissions in Koha are not granular enough to be able to accommodate that. Even without the budget_manage_all permission, libraries can view ALL budgets from Acquisitions > Administration: Budget (from left navigation). Selecting the green hyperlink returns a "No Fund Found" error (correctly). However, the Action buttons are available and libraries can edit another library's overall budget amount and add funds to that budget. They shouldn't be able to do this without the budget_manage_all permission.
To me it sounds like a bug with visibility, not a permission problem?