The average user doesn't have the level of visibility into the system to know that the middlebox is the one causing the problem. Instead whatever changed last g

The average user doesn't have the level of visibility into the system to know that the middlebox is the one causing the problem. Instead whatever changed last gets the blame, regardless of what's actually at fault. So if a user's existing applications set the spin bit "correctly" and a new application does not, the new application will be judged as buggy, not the middlebox which has been working fine until now.