Instagram and Twitter aren't playing nice, and it's annoying users. As the two services compete in the photo-sharing space, Instagram stopped supporting a key Twitter feature that helps display media inside a tweet. The casual user won't notice anything different on the Twitter website. But on Twitter's mobile app, you will notice that Instagram photos are no longer properly formatted to fit.
Why would Instagram spoil the appearance of photos shared on Twitter? Because Facebook-owned Instagram is growing its website and wants you to stay on its app. It's all about money.