Haven't heard that one.
The funny thing is with BA that they mustn't have theoretical seating or restrict certain seats being available to status on the day they checkin. They obviously can restrict it somehow in reservations but possibly around T-80 or later it's possible for the airline doing the checkin for the first (non BA) flight to change pax to a better seat eg row 1 on all Y 767 flight LHR/GLA, row 4 on a 737 flight, row 28 on a 744 or 77W or upper deck on the 388. Same for AA - easy for a non-status pax to get row 8 on a 738 or exit row.
Will have to check it out. Sounds good.
I found Award Wallet advised of a seating change on AA flights where the a/c was still a B757 but had changed from 12DE in an exit to 24AB in an exit when it must've gone from an AA 752 to an old US 752 (had all the US Air livery inside). When I received the email it had a red line through our original seat selection then displayed the new seats. I went straight to the AA website and was able to reselect exit row seats 6DE on the 'new' a/c.
We had this happen to us on a BNE/xSYD/HNL/xSYD/BNE pnr - outbound was July last year and inbound November (nested fare) where we had allocated seats at the time of booking like we always do, then upon checking MMB discovered that 28JK had become a generic window request for both of us. Both of us have been WP for several years and there was no drop in status for etiher of us so I get the feeling it's more a system glitch than anything else. It's possible at some stage that the a/c type HNL/SYD changed from a 332 to 333 then back to a 332 again however the seating SYD/BNE on the 738 also disappeared for the QF552 or QF556 flight which would not have had a a/c type change as always operated by a 738.