Relative layout behavior or creating custom control.

Hello. I'm trying to create message contol wich should look like this: http://imgur.com/bl2HWsf
I think it should be relative layout where I will add CircleImage, Frame with rounded corners and Triangle control, which I already create.
But i faced a strange behaviour of RelativeLayout.
I already asked about this on SO (http://stackoverflow.com/questions/32488428/xamarin-forms-relative-layout-strange-behavior) but didn't get real solution.
So may be here can someone explain me why RelativeLayout can move out of screen bounds or cut content.

Thanks in advance!

PS Maybe someone developed someting similar? Any links will be appreciated.