I am trying to show an ion-ios-close button on a modal window header bar and it would show only with the nightly build but not with any other such as 1.0.0-beta.14.
Nightly includes the latest ionicons. beta14 is still on the older version is the reason why. Use this for beta14 for just now. http://ionicons.com/1.5.2/
Beta 14 shipped with the older ionicons because it still needed the animated loaders.
They have since been removed from ionicons in 2.0 and replaced with animated svg directives in the nightly builds of ionic.