You can see whether availability control is active by looking at the system status of the potential budget object, or the display and change mode in the budgeting function (original budget, release, and so on).
Availability control is active in the following cases:
In The Project System (Same as for Internal Orders)

As well as the assigned and the distributable budget, the system displays the element with budget (which is on a higher level in the project structure) in the Controlling element column for each WBS element without budget. The system posts assigned funds from the WBS element and all lower-level WBS elements (that do not have any budget) to the controlling element.
The current assigned and distributable values are displayed after the budget is checked.