Can’t confirm this, setting cursor mode to Windows still makes this work fine (but only with NUI focus enabled, as otherwise the game will reset cursor to center position! that native can’t be relied on with NUI cursor not enabled, if it works with raw input but doesn’t with Windows mode that can’t be fixed since the game requires the cursor to be reset to center for Windows mode to work, but the script is wrong for relying on that instead of the game’s stick/mouse input control).
I see this particular script indeed uses this without actually using NUI and this is not intended to work indeed, it working with raw input instead is a bug, since GET_NUI_CURSOR_POSITION uses the Windows cursor data which is bypassed for raw input (and with NUI focus on) but is used by the game in Windows input mode.
→ not a FiveM bug, the script is doing something it shouldn’t