RegisterCallback<ClickEvent> triggers twice on Linux only

Hi,

I noticed when using

```
element.RegisterCallback<ClickedEvent>(evt => Debug.Log("Clicked Event"));
```
or

```
element.RegisterCallback<MouseDownEvent>(evt => Debug.Log("Mouse Down Event"));
```

It always triggers twice and ONLY on Linux. No Issue on Windows as far as I can tell.

What works is using a manipulator though:


```
element.AddManipulator(new Clickable(evt => Debug.Log("Clicked Manipulator")));
```
Works like a charm, only triggers once.


So there are two questions:

1. Is this a known bug? Is there some fix for it or workaround other than using manipulators

2. Is there a Manipulator for the MouseDownEvent as a workaround for now?

 

Hi,

my current setup is 2020.3.2f1 and I use the preview 14 of UI and Builder.

As a workaround I tried to subclass https://docs.unity3d.com/ScriptReference/UIElements.Clickable.html and override ProcessDownEvent and in fact that executed twice as well.
So the issue seems to be in the deeper Codebase I guess.

I will report a Bug later!

Btw. I reproduced this on a second machine as well.


And my workaround is now:

```
if (Mathf.Abs(mouseDownEvent.timestamp - lastClick) < 100)
return;

lastClick = mouseDownEvent.timestamp;
```

in my Click Handler to ignore the second click.

Let me know if you know anything better than that.

 

I've reproduced the same behavior on my Linux machine (Fedora 34, KDE, Wayland, latest stable Unity version and the latest UI toolkit).

Any updates?

 

Experiencing this on Manjaro with Unity 2021.2.0b14

 

sadly this bug is still around/reappeared, at least for Ubuntu 22.04 and Unity2022.2.3f1

edit: not only for Click Events but also for every other Pointer Event, like PointerMoveEvent, PointerDownEvent, etc.
the only differences i can see are timestamp where the 2nd event is fired one tick later, and position where is a difference below 0.5 on x and y.