emergency flashers and the interior lights (all of them)

not always but 40-50% of the time. I just switch shut the flasher and the interior lights and all goes back to normal.

It is a feature or some module or switch or something is creeping out ?

This car keeps giving me issues. No big ones yet, but a bunch of little ones. I'm not in love with the E39 for sure. By far the least reliable car I have owned in a past 10 years.
The MB ML430 and the Range Rover tops the list for sure, but those were the wife's car.

Once I had a Mitsubishi Diamante Wagon - most reliable car ever owned - bought in 96 with 10k miles and sold in '99 with 90k miles, spent money on oil, 1 set of brake pads/front rotors and 1 set of tires and 1 tune-up. Nothing else. I did not do any other maintenance on it nor did I fix anything. Never needed fixing. Was decent on gas, fairly oke on speed and it was a perfectly good tool for I needed it. it had a tow hitch and I used to tow jetski's and ATV with it. Loved the car but then got bit by a BMW bug. Bought my 1st 840ci in 1998 and have had 3 more E31's. All pretty reliable, by far more reliable then the E39 528iT for sure.

I guess I picked a wrong one... '99 528iT with 87k miles Silver with grey non-sport. for sale... or trade... soon.

1997 BMW 840CiA
1990 BMW Z1
1999 BMW 528iT (Hauler mobile)
2002 Astro Van AWD
2003 Nissan 350Z Enthusiast Package
1987 BMW 535i with 5spd manual (for sale)
1992 BMW 735iL (needs head and interior)
1977 BMW 320i (project racecar)
2007 Mazda CX9 AWD (Wife mobile)
1998 Yamaha Blaster+Breeze

1995 850CSI CD00177 (SOLD)