Opening 2nd maven project always closes the 1st project in

Preferences/Apperance/system settings,

"Open project in the same window" is selected

open the 1st project

goto File/open, to open the pom file from 2nd project,

open as project

this always closes 1st project, only 2nd project exists in intellij.

How to make both projects exist in the same intellij-idea pls ?