Cannot delete very old CX order

I have a very old CX sell order (CXO bc807371) on IC1, which has never been traded against. I now cannot delete the order - if I press the “delete” button on CXOS, it flashes the “order deleted” green modal, but the order does not clear, and is still there on refresh/reload.

i did this too, deleted an order multiple times and it wouldn’t go away. then i got more warehouse space and it worked

Related to this bug:

The game no longer tells you the cancel order failed because of insufficient warehouse space.