I am having the same problem on a flight for next September. Only in my case, EY actually changed me to a different flight. Originally I was confirmed in F on a A380 operated flight and was moved to F on a A340 operated flight. Expertflyer shows the "equipment change" message.
Just called EY to understand why they changed my flight and the agent said that the system showed the flight as cancelled. However, when she looked at the schedule, the flight is still showing as confirmed. Agent sent a message to their rescheduling department to figure out what happened and said would move me back to the original flight if it is indeed operating.
All sounds very strange, as there is no indication EY is cutting one of the LHR flights.
Will post again when I hear back from EY.