Where do SCVs go inside refineries?

SCV just before it enters the refinery. Its order is 'MoveToGas'.

SCV inside refinery. Notice the info panel is still being drawn in the same place. Its order is now 'HarvestGas'.

The refinery info panel, with SCV inside. BWAPI does not return any units loaded inside the refinery, or else it would have shown up on the info panel.

SCV as it leaves the refinery. Its order is now 'ReturnGas'.

I now believe that the SCV simply turns invisible while it is harvesting gas. Maybe it is also invincible. BWAPI's Unit::getLoadedUnits() cannot be used here as it returns no loaded units. The only way to check for SCVs inside refineries seems to be to see if the Order status is 'HarvestGas'. BWAPI documentation notes that Game::getAllUnits() does not include units inside refineries so the pointer to the SCVs must be saved before they enter.