SideMenu with push to page rather than setRoot

Hello,
I found that the behaviour in sidemen is different when items trigger a “push to page” rather than a “setRoot page”.
When the destination page is set as root: the transition is smooth, no problem.
When the destination is a push: there is a blink effect, the destination page is displayed after being white for a fraction of second.
It can be simply checked with the standard set up:

ionic start myApp sidemenu
app.component.ts:

  • openPage(page) {
    this.nav.setRoot(page.component);
    }
    or

  • openPage(page) {
    this.nav.push(page.component);
    }

I guess it is a normal behaviour, and I don t know the framework enough to know why.
Any enlightenment is welcome…
Thanks
Mat