The Interact With Target mapped key turns off click to move once it has finished. If you don't want it to, then under keymap ISB42 - WoW, you can shift click on the "Click To Move Off" mapped key, so it goes Red, which is disabled.
You can't make hunters act like melee, coz they aren't. IWT will move them to within range for the NPC and the interaction that they will be performing with that NPC. Turning off click to move doesn't affect the movement in progress. They
might move to melee range if they happened to have no ranged weapons. The IWT range seems to more depend on the class, rather than what you happen to have on you. Case in point classes that used to have a wand slot (paladins?), are always a bit weird with IWT.
From an old post
Lax wrote:IWT on classes that originally had a wand slot will be a little flaky. This is built into the game and not much we can change about it other than to work around the issues. I don't remember all of the specifics, but MiRai and I did some testing specifically on this a few months ago. Something like, if you have a wand equipped IWT will not face the target, but if you have a melee weapon equipped it will work as long as you're in melee range OR outside of ranged casting range. I remember something about the distance to the mob mattering. So anyway if you run up to the mob and your front guy is in melee range and the rest are in casting range, this would mean the toons in the back don't work right.