Instagram photos aren’t displaying properly on Twitter. It could be a bug, it could be another escalation of the ongoing spat between the two companies that’s been going on more or less since Facebook bought Instagram.
If it’s a conscious and permanent decision by one of the two companies, it’s disappointing. End users just want the two apps to play nicely together.
Update: A Facebook rep confirmed to AllThingsD that yes, Instagram disabled support for Twitter cards.