Scenario:

• Key in hand, outside of the car (nothing in pocket pressing lock button)
• Unlock car with the unlock button - two beeps and the car unlocks
• 60 seconds later, the car relocks all four doors and the trunk, but without the normal 3 beeps

Car has keyless entry and go, it also has a trunk closer that is basically worthless. It used to just go part way and then reverse, unless I assisted it. Now it actively fights me in the opposite direction (opening or closing) They keyless door handles and trunk closer on this car have been an absolute nightmare. Replaced multiple door handles multiple times and have since given up and simply don't use the feature. Getting sick of this piece of **** after 9 years and 110K miles.

The relocking function is standard feature on MB for last 30 years.
It prevents accidental leaving the car unlocked by stuff in your pockets pushing the remote.

Umm
no

Edit: Well I'll be dipped in ****. It does indeed relock after 60s. Leave the car unlocked when you remove the key, it'll stay unlocked. Lock the car with the fob, unlock it with the fob, and 60s later it relocks.
I wonder if that can be programmed out of it with STAR.
No Keyless Go on my car.

Mine has always done that

My E63 does it as well. It's normal.

E320 cdi 2003 does it well

Yeah 2005 E320 CDI does it. When I go to work on it just open the drivers door, that will deactivated and stay unlocked until you lock it again or drive it. Not sure if you can turn it off in Xentry.
I would think you can since mechanics would unlock your vehicle and leave the keys in the vehicle or on a key rack.
Basically its what rapidoxidation said you unlock the Mercedes it will re-lock if nothing is done, you leave the vehicle (turning it off and not locking it) it will stay unlocked.
So I just unlock then open and close the drivers door, I only do this when I work on it.

Have you tried switching off the auto lock in settings??