Oof, that was ugly: The full-screen image picker left the New Post view in the responder chain, so all its key commands were still active. When I hit Esc to try to cancel out of the image picker, it nuked the whole post!
Worked around it by only adding the shortcuts when the view is visible. Feels like I'm fighting the system a bit - maybe Cancel should make you confirm first when there's content you'd be losing? (It doesn't because, eventually, it should just autosave a draft…)
Why doesn't Esc dismiss modals all across the iPad, though? Weird that's not default behavior! (I mulled doing Cmd-. too, but figured Esc is enough.)