Transform Tool Issues — Selected object has thick black border

Hello!

I'm experimenting with a simple 2d stick animation. I have rigged the stickperson so each appendage section controls the section below it. One of my sections (lower leg) I can no longer rotate using the Transform Tool. And when I select the lower leg, the object now has a thick black border around it. Normally the transform tool shows as a thin black border. Please see the attached image. Transform is set to "free transform". I checked the object's properties and everything seems normal. Can't figure this out, please help!