Reproduction steps:
1. Open attached project (Cursor.zip)
2. Open "3D Objects" scene
3. Hit play
4. Press "space" to lock the cursor
5. Press "space" again to unlock the cursor

Expected result:
Cursor is centered (points to red small cube)

Actual result:
Cursor is above screen center

Note:
5.4/5.5b documentation states: "When locked, the cursor will automatically be centered on view", hence it should appear centered when unlocked.

Reproduced on 5.2.5f1, 5.3.3f1, 5.4.3p1, 5.5.0f1, 5.6.0a3