I noticed this aswell, its quite obvious both in sandstorm and on the source version.
But to me it seemed like this was added on purpose, the feature originally called lazy aim.
Suppressing people with tracer rounds in the source version was supposed to give suppressed combatants more lazy aim, so it would make hipfire harder for them.
This entire lazy aim schmutz was made for hipfire, thus why it isn't present when aiming down the sights.
Nevertheless, i dont like it, it messes up aim and feels weird.