Hi Eric (or anyone else!),
I've built an MRAID compliant ad and am successfully using mraid.useCustomClose(true)on iOS to hide the default close button and display my own in the Interstitial Example app, implementing version 6.6.1 of the AdMob SDK.
Unfortunately, the behavior differs when the same ad is shown through an Android app (I've tried both the Advanced sample app as well as the Interstitial Example.) For Android I'm using AdMob SDK v. 6.4.1. From within the ad after it has expanded, I can getExpandProperties and see that useCustomClose is true, but the default close button remains visible on Android < 4.4.2.
I can also confirm that mraid_app_interstitial.js is calling AFMA_SendMessage('customClose', {"custom_close":1})
Can you think of any reason custom close would not be supported on Android using version 6.4.1 of the AdMob SDK?