I was doing the Kol fight yesterday, which is a very lengthy DE event in which you can easily alt + tab while autoshotting as long as you stay on maxed ranged.
Anyway, during that encounter I noticed that auto-shot would sometimes turn off, despite the target still being in effective range. I was getting annoyed at this until I realized it was connected with the range indicator under the skills (they have a little red bar if a target is out of range).
The thing is, I could still hit the target for damage (using a Short-bow) another 3-4 yeards beyond the effective range indicated by the game. I haven’t yet checked this on other abilities but it seems like the range indicators are off.