[KBM] Remapping modifier key (Alt/Ctrl/Shift) to non-modifier key causes target key to be delivered as WM_SYSKEYDOWN

[oMatheusmol]

Microsoft PowerToys version

0.83.0

Installation method

GitHub

Area(s) with issue?

Keyboard Manager

Steps to reproduce

1. Open PowerToys Settings → Keyboard Manager → Remap a key
2. Set source: Left Alt | target: Backspace
3. Open any text editor and type some text
4. Press Left Alt (remapped to Backspace)

✔️ Expected Behavior

One character is deleted per keypress, identical to pressing the physical Backspace key.

❌ Actual Behavior

The entire previous word is deleted instead of a single character. This happens because the injected Backspace event is delivered to applications as WM_SYSKEYDOWN (Alt+Backspace) instead of WM_KEYDOWN (Backspace), since the Alt modifier state is still active at the time SendInput is called inside the low-level keyboard hook callback.

Upload Bug Report ZIP-file

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Additional Information

No response

Other Software

Windows 10 Pro 24H2 (Build 26100.8037)