Not sure what day you are flying but a quick google shows that it always has been an IB operated flight. Clearly just a BA IT department glitch- again.

First couple of hits are to Flightradar and Flightaware which show the flight as being operated by IB. Seems to be a mixture of 320 and 321 over the last 20 days or so with the odd 319.

The flight code also shows its IB operated. IB's flights on BA metal tend to be flight numbers IB74XX where as IB operated flights are IB31XX and IB Express is IB37XX.