I'm a little confused by the behavior of the CGA cursor.

I was informed by a BIOS developer that I'm showing a single pixel tall cursor at the top of the screen in my emulator where the cursor shouldn't be visible.
This is also present in the menu of CGA_COMP where the cursor should be hidden. This is a condition where CursorStartLine = CursorEndLine = 0 and the cursor attribute bits are 00.

If this would hide the cursor, great. But the issue is my own test program shows that it does not:

This code just does
mov ax, 000Ah ; Set CursorStartLine to 0
out dx, ax
mov ax, 000Bh ; Set CursorEndLine to 0
out dx, ax

Is there some other condition necessary to hide the cursor in this case?