I think it has always been that way on my 2015 Model S. It is annoying if, for example, you are doing something in your car and need the light.
Here is what the Model S manual says. Apparently it will stay on for up to an hour if you turn it on manually.
"If you turn on DOME lights, all interior dome (map) lights turn on when you unlock Model S,
open a door upon exiting, or shift into P (Park). They turn off after 60 seconds, when you lock
Model S, or when you shift into a driving gear. If set to AUTO, dome lights turn on only when
little or no light is detected.
"You can also manually turn an individual dome light on or off by pressing its lens. If you
manually turn a dome light on, it turns off when Model S powers off. If Model S was already
powered off when you manually turned the light on, it turns off after 60 minutes."