I have the same scenario. When I run the Profit and Loss Budget Report and choose the "Expanded" button to filter the dimension/cost centre... the system only filters the data on the "Actual" column.
The column for Budget amount shows the total for all cost centre.
Example: CC1: $500 and CC2: $300
When I run the P&L budget report for CC2 the budget column shows: $800 and but the actual column is correct (only the total for CC2 is shown).
I think this is a bug in the report