As noted above each key contains different stored memory data for the seat.
Originally Posted by GeorgeT
Does someone else drive your 5? If so the seat will return to the last position that it was in when that key was used.
Does the Memory light come on (red) when you try setting the memory?
You can also turn off (uncheck) the "Last Seat Position" in iDrive so the seats won't respond when a different key is used.
2012 BMW 535i X-drive; Space Grey/Black Dakota, Fineline; Executive (Auto trunk, NAV, HiFi Prof, Lumbar, Rear Cam, SIRIUS, Voice), Technology (Blind Spot, Hi-Beam Assist, Lane Departure, Surround View), APPS, Rear heated seats, Tint.
Retired: 78 300D, 81 300SD, 87 190E, 88 Porsche 924, 89 260E, 93 300E, 97 Volvo 850, 98 E320, 03 BMW 325iT, 02 C230 Sport Coupe, 08 BMW 535i