I've been playing since the release of F2P, and every time I've encountered a Heavy Plasma Torpedo, (The "High Yield" targetable ones that the Romulans are fond of) I've just braced for impact and redirected my shields.
Just a few minutes ago, I discovered something that I didn't read anything about anywhere.
I was in an NX-01 class ship, just messing around, playing "Shaharian's Swords" and the last ship launched three of those Heavy Plasma torpedoes. I panicked, and pressed "Evasive manuvers" to try to run away from them.
To my surprise, the torpedoes redirected back at the Romulan!!!
I mean, not one of em hit me. It's like when they couldn't turn fast enough to catch me a couple seconds later, they just turned around and went back at the Romulan!
I think for it to work, you need to be close to the ship, so the torpedoes don't just dissipate when they can't hit you. After a bit, they should turn around and head for the Romulan ship.
I don't know if this was a glitch, or intentional, but someone else, try it, and lemme know if you can do it! It would be awesome if I discovered a new way to evade them!
Oh, and sorry if this is old news, and I'm an idiot.
I'm pretty sure that if you get out of range of a targetable torpedo or mine, then it loses its lock on you and then finds another target if there are any within range. There is however a bug that allows such torpedoes to lock on to what ought to be friendly ships when they acquire a new target (such as your example of the Romulan torpedoes returning to the ship that launched them).