This piqued my interest, so I thought I would actually test things out. I'm fairly certain that the OOR messages work differently than I remember they did in EoF beta when I did my tests last. Not really doing a study on it, they seemed to trigger 1-3 times a second at irregular intervals. Somewhat strange.
Anyhow, I used a little tool that I already had which was a long abandoned "Swing Meter" plugin for ACT.
Using a 4.0s weapon, it more or less correctly swings each time... though it's oddly early a lot. Could be rounding on the number EQ2 reports plus lag or something... it doesn't matter.
Anyhow, if being out of range fully consumed an auto attack, the purposely late swings would always be late in a multiple of ~4000ms. Clearly that's not the case, but it's strange how often it would be be late around the same amount each time. I certainly didn't attempt to do that. So it would seem that being OOR only partially consumes an auto attack but coming into range is not an instant attack either.
I think I mentioned this somewhere else, but I'll do so again here. A swing meter like the plugin I abandoned long ago has two major drawbacks. To be accurate with haste, the log file would have to be populated with haste or weapon delay pretty often. I suppose you could set up a chat channel that you cannot see to supply this information to ACT, but it's messy no matter what. Secondly and most importantly, ACT cannot tell the difference between two weapons of the same type. This would make it useless for anyone dual wielding with two piercing weapons for instance.