Item counts display the network-wide total (MEGA Bulk Cells + other drives), consistent with the actually extractable amount — the number never jumps when extracting.
Auto-marking of MEGA Bulk Cells
The first time an item is inserted, if no bulk cell accepts it, the terminal automatically writes that item's mark onto an unmarked MEGA Bulk Cell and retries the insertion;
Inserting the same item again hits the marked cell directly, with no extra cost;
Which cell gets marked follows the priority configured in the drive GUI (highest priority first);
Auto-marking can be turned off in the terminal settings, reverting to vanilla MEGA behavior; the toggle is persisted.