Spring @SessionAttributes shared between controllers?

Question

I'm using Spring 4.3.7, and I got two form controllers with forms rendering using Spring form taglib in corresponding views. To preserve form data between requests (for rendering invalid forms) I store them in SessionAttributes.

LabCreateController:

@Controller
@RequestMapping(path = "/labs/create")
@SessionAttributes("form")
public class LabCreateController {

    @ModelAttribute("form")
    public LabCreateForm form() {
        return new LabCreateForm();
    }

    @GetMapping
    public String showForm() {
        return "lab_create";
    }

}

WallController:

@Controller
@RequestMapping(path = "/group/{id}/wall")
@SessionAttributes("form")
public class WallController {

    @ModelAttribute("form")
    public PostCreateForm form() {
        return new PostCreateForm();
    }

    @GetMapping(path = "/new")
    public String newPostGet() {
        return "communities_newpost";
    }

}

I open /labs/create in browser, everything is fine. Then I open /group/4/wall/new and get a following error:

Invalid property 'text' of bean class [...LabCreateForm]

i.e it means that attribute form from LabCreateController somehow passed to WallController, though Spring documentation says:

Session attributes as indicated using this annotation correspond to a specific handler's model attributes.

I believe it means they shouldn't be shared between controllers. Also this answer says that it is so since Spring 3.

Is it a bug or I'm missing something? If not, what is the appropriate way of storing a form inside one controller?