Unfortunatly, that was one of the "features" SOE added in LU12
[Patch Notes] :
- Hitting a function key a second time will now target that character's pet. For example, hitting F2 once will target that group member. Hitting F2 again will target that player's pet.
But I think you found a great workarond using /target_none first. If you are looking for something to use as a pause in a macro I like to use the Catalogue Creature skill. As far as I know any class can get it as soon as they get a catalogue quest, it has a 3 sec cast time, and it can be used both in/out of combat.