I noticed missing error notifications (small error icons used for example at ref. attributes) when working with design view elements like step/flow/decision that have an id attribute. In source view we can see there is an error on line where id is duplicated, but not in design view, see attachments (source view: error icon on second occurence of my-step-listener, in design view this does not work).

P.S. Do not notice duplicated messages in Problem view, it's been already reported.