If you're shooting a specter it usually means an unclean connection loss, not a menu log out. Ships using the menu disappear almost immediately after the timer and take damage almost to the end, while a disconnection requires the ship to time out, which can take several seconds during which no damage is taken and the last input is usually repeated.
A ship flying straight doesn't necessarily mean they are logging off either. If the velocities of the vessels in question are close enough and the pursuer doesn't have long range weapons, fleeing in a straight line, as risky as it is, may be the only way to open up distance. Also, if a ship's thrusters are disabled or unpowered (either from damage or during a reboot) the ship will be adrift, flying in a straight line on whatever vector it had prior to the thrusters shutting down.
Indeed, I regularly encounter situations where a logout or disconnection is assumed, and people turn back, when, in reality the vessel being perused just went dark.
Here's an example:
My wingman was pulled over, fought his attacker for a bit, had his thrusters shot out, after which the attacker apparently left when he couldn't immediately reacquire contact...either that or he specifically left the ship stricken as bait for my CMDR, but that's a far less likely scenario as it requires a string of unlikely assumption to be true.
Still not a counter to the time wasted prior to them disconnecting/logging out.
My CMDR has been in situations where he's chased, or been chased, for hours...sometimes across multiple sessions, and either side would rightly have been irked if the climax of the encounter was the other party deciding they've misjudged and logging off instead of escaping or being shot down via in-game means.
I'm extremely doubtful of this.
As a player whose CMDR rarely initiates hostilities and almost never carries an interdictor, almost all of the deliberate disconnecting, and most of the menu logging, I see are on the part of the aggressors.
Combat logging needs to be recognized for what it is...not an understandable action when confronted with apparent griefing, but as a prime griefing tool, habitually used to undermine the legitimate gameplay of others.