They've always been stripped for me as well. This "emoji" actually appears black for me however.

I think the reason its not stripped is because it's actually "U+2665 : BLACK HEART SUIT {valentine}" which predates the emojis. Lots of fonts and OSes will render these older unicode symbols as emojis

Well, in theory, with proper UTF-8 support you don't need to filter out anything.

Unsupported unicode code points are just rendered using a place holder.