A single mouse event "leaks" into chained clients when moving back

[hoshinolina]

Let's say I have three chained clients like this:

     +---+
     | C |
     +---+
+---++---+
| A || B |
+---++---+

The mouse is connected to A, which then has a client declaration for B, which then has a client declaration for C.

When the mouse is moved from A to B to C, things work as expected. When the mouse moves back from C to B, that works fine. However, when the mouse moves from B to A, the mouse pointer in C (which at this point is at the bottom of the screen, where it was left after B took control back) moves by an amount that seems to be equal to the mouse event that crossed over from B to A (to the left). In other words, somehow, the mouse events are momentarily directed to C again when crossing back from B to A.

This only happens once. Moving back to B and again to A does not leak any events to C. It's only the first time after leaving C, then leaving B, that an event leaks. To make it happen again, I need to move the mouse all the way to C one more time.

[feschber]

Could you add which backends are being used on the three devices?

[hoshinolina]

This is running on KDE Plasma Wayland on all three machines, with the default backends, which it reports as:

[2025-11-02T12:03:27Z INFO  input_emulation] using emulation backend: libei
[2025-11-02T12:03:28Z INFO  input_capture] using capture backend: input-capture-portal