`to_if_held_down` action triggers prematurely

[gregorias]

Setting a variable in a to action and unsetting it in to_if_held_down may cause the variable to never be set for low values of to_if_held_down_threshold_milliseconds.

Reproduction

1. Add the following complex modification:

{
    "description": "testtest",
    "manipulators": [
        {
            "from": { "key_code": "q" },
            "to": [
                {
                    "set_variable": {
                        "name": "layer-q",
                        "value": 1
                    }
                },
                {
                    "set_variable": {
                        "name": "layer-q-start",
                        "value": 1
                    }
                }
            ],
            "to_after_key_up": [
                {
                    "set_variable": {
                        "name": "layer-q",
                        "value": 0
                    }
                },
                {
                    "set_variable": {
                        "name": "layer-q-start",
                        "value": 0
                    }
                }
            ],
            "to_if_alone": [{ "key_code": "q" }],
            "to_if_held_down": [
                {
                    "set_variable": {
                        "name": "layer-q-start",
                        "value": 0
                    }
                }
            ],
            "type": "basic"
        }
    ]
}

2. Set to_if_held_down_threshold_milliseconds to 110 ms or lower.
3. Open Karabiner-EventViewer and the variables tab.
4. Press and hold q.

Observed behavior

(Not 100% reliable, decrease to_if_held_down_threshold_milliseconds to increase chances.)

You’ll see that layer-q gets set to 1 but layer-q-start remains at 0.

I have recorded my view as I continuously press q:

Screen.Recording.2026-02-20.at.07.01.15.mov

Most of the time, I trigger the bug.

Expected behavior

layer-q-start flashes to 1 for the duration of to_if_held_down_threshold_milliseconds.

Notes

• Increasing to_if_held_down_threshold_milliseconds resolves this issue.
• This behavior breaks my hold-tap layer causing it to lose keys during fast typing.