[Bug] `AUTO_SHIFT_MODIFIERS` occasionally sends single key instead of with-modifier-variant

Describe the Bug

Since I've enabled AUTO_SHIFT_MODIFIERS, I have the issue that ~5% of all uses/presses of e.g. CTRL+c (copy to clipboard) just send a c instead of CTRL+c.

I thought it might be that I unintentionally press CTRL+c for too long (longer than AUTO_SHIFT_TIMEOUT, which is 150ms in my case), and thus it sends CTRL+SHIFT+c (as expected, when you press it for too long), but this is not the case: it doesn't send CTRL+SHIFT+c, but actually only c.

Seems like a bug to me. Here is my keyboard code. Any ideas?

Keyboard Used

sculpter

Link to product page (if applicable)

No response

Operating System

Windows 10

qmk doctor Output

No response

Is AutoHotKey / Karabiner installed

• AutoHotKey (Windows)
• Karabiner (macOS)

Other keyboard-related software installed

No response

Additional Context

No response