Don't stop Duplicating when ALT is released !!
When using Select and Direct Selection Tools, you can duplicate elements by holding ALT-key down.
But if you release the ALT-key before you release the Mouse Button, the duplicating ceases . This differs from how most of the other applications behaves. For example in Photoshop, duplicating continues even if you release the ALT before you release mouse button.
How this works in Illustrator leads often to situations where you think you have duplicated something, but you actually just moved it. And often I edit the element I thought I duplicated, and loose lot of work as it wasn't actually duplicated and I edited the original.
I can't believe how many this kind of little annoying things Illustrator has. Every time I have to use it, my day is ruined. This is one of those days. I can't understand how a developer with size and budget like Adobe can't get these fixed.
There is a controversy about modifiers. See, Photoshop requires you to start holding Alt/Opt before you click, only then it counts as duplicating. While it clearly defines the intention and allows a user to release the Alt any time, it's also infuriating for those who comes from the Ai and other apps first, where you can start holding Alt/Opt anytime, and duplicating is intended only when the key is held at the moment of releasing. If one decides not to copy, they can just stop holding... but this requires to time the release.
These are two different worlds and there is no clear intersection between. But perhaps an option can be introduced to control it.
Anyway, thank you for raising this up. Let's hope more users come to talk about it.