java - Previous Activity closes when starting new Activity -

i have odd phenomenon.

in mainactivity have button, starts new activity.

i used:

intent myintent = new intent(mainactivity.this, secondactivity.class); startactivity(myintent); 

the second activity has small imageview , background transparent. when button clicked, second activity should overlay mainactivity, should seen in background.

it work on phone (api level 21) not on friends 1 (api level 19). on phone works should. on friends phone mainactivity closes , there imageview , background picture of phone. how can prevent mainactivity gets closed on phone when starting second one?

thanks help.

also, in android manifest.xml can set lowest version of android, may problem?