Did some searching and couldn't find a thread on this, so here is my question/bug report. I specifically noticed this in the Vacuum Mod but I'm nearly certain it works in Vanilla.
When an enemy is targeted by the player, and then the player loses sight of the enemy; upon re-entering sight range the targeting lock is still applied. This means missiles still track, etc.
However, when the player goes into 'follow target view' mode (Z-key) and then the player loses sight, the targeting lock is lost and even upon re-entering sight range it is not applied.
This is particularly annoying if you are bombarding from a long range using missiles, relying upon allied fighter wings to provide sight, and using Z to gauge effectiveness of your bombardment; but overall it seems that the targeting lock system works differently when it should be the same regardless of what screen you're focused on at the moment of sight loss.